Frugivore assemblage of <Emphasis Type="Italic">Ficus superba</Emphasis> in a warm-temperate forest in Yakushima,Japan

Understanding fig consumption patterns is important because figs are regarded as a keystone resource for many frugivorous species in the tropics. While much work on fig consumption has been conducted in tropical regions, temperate forests are particularly interesting for study owing to pronounced seasonal variations in temperature and community-level fruiting phenology. We studied frugivore consumption of Ficus superba (Miq.) Miq. var. japonica Miq syconia in a warm-temperate forest in Yakushima, southern Japan. We conducted 141 4-h focal observations of fruiting F. superba trees over 12 months. We aimed to assess the relative quantitative contribution of each species of frugivore to F. superba consumption over a year as well as factors affecting seasonal variation in consumption. Japanese macaques were by far the most important F. superba syconia consumer (87.6 %), followed by brown-eared bulbuls (5.0 %), and varied tits (4.2 %). Japanese macaques increased their F. superba consumption when the temperature was high and fruit availability (F. superba and other species) was low. Macaques seemed to avoid searching for rare F. superba trees during winter and used F. superba syconia as a fallback food during fruit scarcity. Birds showed the opposite pattern: they increased F. superba syconia consumption when the temperature was low and fruit availability was high. This was probably because birds eat insects as their main food in the summer and switch to fruit as autumn turns to winter.     

Regional chronologies of <Emphasis Type="Italic">Cedrela</Emphasis><Emphasis Type="Italic">fissilis</Emphasis> and <Emphasis Type="Italic">Cedrela angustifolia</Emphasis> in three forest types and their relation to climate

Key message

Although tree-ring chronologies of Cedrela fissilis and Cedrela angustifolia showed a common climatic signal, local conditions influence growth, suggesting that forest guidelines should be appropriate to the species and context.

Abstract

Cedrela species are highly valued because of the quality of their timber. Understanding the behaviour of each different Cedrela species and their ecology is of importance to ensuring that forest harvesting and management do not endanger the survival of natural populations. These species grow in a wide range of environmental gradients and different types of forests in Bolivia. This study used dendrochronological methods to analyse growth–precipitation relationships of two Cedrela species coming from three locations with different environmental conditions: dry Chiquitano (Concepción), Chiquitano transitional Amazonian (Guarayos), and Bolivian-Tucuman montane forests (Postrervalle). The rainy season in all locations runs from October to April and the dry season runs from May to September. Twelve Cedrela fissilis specimens were sampled from dry Chiquitano, 11 Cedrela fissilis specimens from Chiquitano transitional Amazonian, and 30 Cedrela angustifolia specimens from Bolivian-Tucuman montane forests. The samples were crossdated and exhibited a common signal between trees from three sites, despite tree rings from the Chiquitano transitional Amazonian forest being narrower and displaying blurred bands of parenchyma in the boundaries. Significant inter-series correlation was found for the C. fissilis species series from dry Chiquitano with r = 0.261 (p < 0.01) and Chiquitano transitional Amazonian forests with r = 0.284 (p < 0.01), and for Cedrela angustifolia from Bolivian-Tucuman montane forests with r = 0.374 (p < 0.01). Mean annual growth was 2.07, 1.92, and 2.82 mm year^?1 at the three sites, respectively. Cedrela species from dry Chiquitano and Bolivian-Tucuman montane forests were sensitive to precipitation from October to April of the current growth year (wettest season) and to low temperatures from May to July of the current growth year (driest season). Samples from Chiquitano transitional Amazonian were more sensitive to precipitation during late rainy season (March, April, and May of the current growth year) and high temperatures during the rainy months (November–December). Growth differences between sites and species in response to climate variations and local conditions should be taken into account and handled with different forest management guidelines.

     

NtRING1, putative RING-finger E3 ligase protein,is a positive regulator of the early stages of elicitin-induced HR in tobacco

Key message

NtRING1 is a RING-finger protein with a putative E3 ligase activity. NtRING1 regulates HR establishment against different pathogens. Loss-/gain-of-function of NtRING1 altered early stages of HR phenotype establishment.

Abstract

Plant defence responses against pathogens often involve the restriction of pathogens by inducing a hypersensitive response (HR). cDNA clones DD11-39, DD38-11 and DD34-26 were previously obtained from a differential screen aimed at characterising tobacco genes with an elicitin-induced HR-specific pattern of expression. Our precedent observations suggested that DD11-39, DD38-11 and DD34-26 might play roles in the HR establishment. Only for DD11-39 a full-length cDNA sequence was obtained and the corresponding protein encoded for a type-HC RING-finger/putative E3 ligase protein which we termed NtRING1. The expression of NtRING1 was upregulated upon HR induction by elicitin, Ralstonia solanacearum, or tobacco mosaic virus (TMV) in tobacco. Silencing of NtRING1 remarkably delayed the establishment of elicitin-induced HR in tobacco as well as the expression of different early induction genes in tissues undergoing HR. Accordingly, transient overexpression of NtRING1 accelerated the HR launching upon elicitin treatment. Taking together, our data suggests that NtRING1 plays a functional role in the early establishment of HR.

     

Boreal peat properties link to plant functional traits of ecosystem engineers

Aims

Warming has the potential to alter plant litter mass loss and nutrient release during decomposition. However, a great deal of uncertainty remains concerning how other factors such as litter species or substrate quality might modify the effects of increased temperature on decomposition. Meanwhile, the temperature sensitivity of plant litter decay in tropical and subtropical forest ecosystems remains poorly resolved.

Methods

This study was designed to assess the effects of experimental warming on litter decomposition and nutrient release of two contrasting tree species (Schima superba and Machilus breviflora) by translocating model forest ecosystems from the high-elevation sites to the lower-elevation sites in subtropical China. Translocating model mountain evergreen broad-leaved forest (MEBF) to the altitude of 300 m and 30 m increased the average monthly soil temperature at 5 cm depth by 0.88 and 1.84 °C, respectively during the experimental period. Translocating model coniferous and broad-leaved mixed forest (CBMF) to the altitude of 30 m increased the average monthly soil temperature at 5 cm depth by 0.85 °C.

Results

We found that experimental warming accelerated litter decomposition in both model forest types, and the promoting efficiency was greater when the temperature increased. The litter with high quality (Schima superba) had stronger response to warming than low quality litter (Machilus breviflora). Warming accelerated Na, K, Mg, P, N and Ca release from Schima superba litter, but only simulated Ca release from Machilus breviflora litter. Overall, litter decomposition was controlled by the order: soil temperature > litter quality > soil moisture > litter incubation forest type under experimental warming in the subtropical China.

Conclusion

We conclude that leaf litter decomposition was facilitated by experimental warming in subtropical China. Litter species might modify the effects of increased temperature on litter decomposition; however, forest type has no effect on litter decomposition.

     

Alteration of soil properties by the invasive tree <Emphasis Type="Italic">Psidium cattleianum</Emphasis> along a precipitation gradient on O'ahu Island,Hawai'i

To test the effects of invasion by strawberry guava trees (Psidium cattleianum) on the forest soil ecosystem, we compared soil properties between pairs of adjacent native and P. cattleianum stands. We set up six study sites that had developed under different mean annual precipitation levels in the Ko'olau Mountains on the island of O'ahu, Hawai'i. Accumulated litter mass and soil pH decreased with precipitation in the native stands. Invasion by P. cattleianum increased the amount of litter and reduced the differences in soil water content and pH among the sites. We compared the decomposition process using the Tea Bag Index, which is determined by the difference in dry mass of commercially available green and rooibos teas in nylon mesh bags before and after 90 days of burial. Psidium cattleianum increased the initial litter decomposition rate irrespective of precipitation and other soil properties. On the other hand, P. cattleianum increased the long-term litter stabilization factor of the Tea Bag Index in wetter sites. The accumulation of litter was likely caused by indirect effects of P. cattleianum through the alteration of soil moisture properties. In summary, this study shows that invasion by P. cattleianum could alter the soil properties in both wet and mesic sites, suggesting the possibility of change in composition and/or function of decomposers.     

Influence of environmental variation on the pollination of the ambophilous sedge <Emphasis Type="Italic">Rhynchospora ciliata</Emphasis> (Cyperaceae)

In typically anemophilous families, there are species, such as Rhynchospora ciliata (Cyperaceae), in which both wind and insects have been registered as pollen vectors (ambophily). However, the contribution of each vector to pollination of ambophilous species can change under different environmental conditions. Therefore, this study aimed to determine the primary pollination system, abiotic or biotic, of R. ciliata, comparing wet and dry seasons. We tested the following hypotheses: (1) in dry months, wind is the main pollen vector of R. ciliata; (2) in wet months, insects will contribute more to the reproductive success of R. ciliata and compensate for low fruit formation by the abiotic vector. Our hypothesis was not confirmed. We found that higher wind speed can favor pollination by wind in R. ciliata even in wetter months. Because insects were less susceptible to environmental variation, they contributed more in dry months when wind speed was low, thus compensating for lower fruit set by wind. High rainfall and humidity can result in faster settling of pollen grains suspended in the air; however, rainfall does not prevent pollination by wind. Since individuals of R. ciliata are located near the edge of the forest, grouped quite close together, and as the inflorescence is located at the apex of the floral scape, wind can act as pollen vector and the inhibiting effects of rainfall can be minimized. The contribution of each pollen vector is important to the reproductive success of R. ciliata and the effectiveness of wind varies with local environmental conditions.     

模拟降水分配季节变化对南亚热带常绿阔叶林凋落物的影响

为探讨降水季节分配的变化对南亚热带常绿阔叶林凋落物的影响,在广东省鹤山国家野外生态观测站模拟干季更干(DD)和延长干季(ED)的野外降水控制实验,对森林生态系统中凋落物变化进行了分析研究。结果表明,该试验林年凋落物总量为9.24 t hm–2,在不同时期均以叶凋落物为主,约占50.7%~69.3%。DD处理显著减少了干季(10–3月)叶凋落物量(P0.01)。虽然DD处理下全年总凋落物量比对照降低了10.3%,但差异不显著。ED处理也减少了春季(4–5月)的叶和花果及总凋落物量,全年总凋落物量则比对照增加了11.3%,但ED处理对春季和全年凋落物量的影响均差异不显著。两种干旱处理对凋落物叶质量总体上影响不明显,但DD处理显著减小了火力楠(Michelia macclurei)凋落叶的木质素含量。因此,降水格局的变化可能会影响南亚热带森林土壤的碳汇能力。     

Leaf functional trait responses to changes in water status differ among three oak (<Emphasis Type="Italic">Quercus</Emphasis>) species

We monitored differences in rates of foliar carbon-compound increases with progressive drought as an indicator of sink limitation status and subsequent drought tolerance. We postulate that species which increase foliar carbohydrates and protein-precipitable phenolics (PPP) more quickly than related species over the same time period and drought conditions have stronger sink limitations and are therefore less drought tolerant. Quercus macrocarpa, Q. shumardii, and Q. virginiana saplings were subjected to two treatments for approximately 3.5 months: (1) watered, which received the equivalent of average weekly precipitation for College Station, TX, USA, and (2) droughted, in which precipitation was reduced by 100%. Q. virginiana’s photosynthesis (A) and stomatal conductance (g_s) were 44 and 54% greater, respectively, than the other species in the drought treatment. Q. virginiana’s g_s also increased more dramatically with watering and subsequent increases in predawn leaf water potential. This plasticity suggests Q. virginiana is best equipped to deal with sporadic rainfall events and soil moisture changes, at least in the short term. Results indicate that the three species allocate carbon from photosynthate in different ways. Q. shumardii had the most soluble sugar in its foliage but had the least PPP, while Q. virginiana and macrocarpa had more PPP and less sugar than Q. shumardii. Diameter:height growth rate was greatest in Q. shumardii. Foliar protein-precipitable phenolic content appears to be more affected by factors other than drought. Differences in species’ physiological responses to drought may result in stand composition shifts with future climate alterations.     

Modeled Effects of Climate Change and Plant Invasion on Watershed Function Across a Steep Tropical Rainfall Gradient

Climate change is anticipated to affect freshwater resources, but baseline data on the functioning of tropical watersheds is lacking, limiting efforts that seek to predict how watershed processes, water supply, and streamflow respond to anticipated changes in climate and vegetation change, and to management. To address this data gap, we applied the distributed hydrology soil vegetation model (DHSVM) across 88 watersheds spanning a highly constrained, 4500 mm mean annual rainfall (MAR) gradient on Hawai‘i Island to quantify stream flow at 3-h time-steps for eight years in response to the independent and interactive effects of (1) large observed decrease in MAR; (2) projected warming and altered precipitation; and (3) four scenarios of forest invasion by the high water-demanding non-native tree species Psidium cattleianum. The model captured 62% of variability in measured flow at daily time scales, 95% at monthly time scales, and 98% at annual time scales. We found that low DHSVM modeled flow (Q ₉₀) and storm flow (Q ₁₀) responses to observed declines in rainfall dwarfed those of projected temperature increase or invasion, with flow decline positively correlated with MAR. As a percentage of streamflow, temperature and invasion reductions were negatively correlated with MAR. By comparison, warming alone had little effect on Q ₉₀ or Q ₁₀, but both decreased with increasing P. cattleianum cover, and projected effects of declining MAR were accentuated when combined with P. cattleianum and warming. Restoration mitigated some effects of climate warming by increasing stream base flows, with the relative effects of restoration being larger in drier versus wetter watersheds. We conclude that potential changes in climate in tropical environments are likely to exert significant effects on streamflow, but managing vegetation can provide mitigating benefits.     

Prevalence and Seasonality of the Amphibian Chytrid Fungus <Emphasis Type="Italic">Batrachochytrium dendrobatidis</Emphasis> Along Widely Separated Longitudes Across the United States

The chytrid fungus Batrachochytrium dendrobatidis (Bd) has been implicated in amphibian declines on almost all continents. We report on prevalence and intensity of Bd in the United States amphibian populations across three longitudinally separated north-to-south transects conducted at 15 Department of Defense installations during two sampling periods (late-spring/early summer and mid to late summer). Such a standardized approach minimizes the effects of sampling and analytical bias, as well as human disturbance (by sampling restricted military bases), and therefore permits a cleaner interpretation of environmental variables known to affect chytrid dynamics such as season, temperature, rainfall, latitude, and longitude. Our prevalence of positive samples was 20.4% (137/670), and our mean intensity was 3.21 zoospore equivalents (SE = 1.03; range 0.001–103.59). Of the 28 amphibian species sampled, 15 tested positive. Three sites had no evidence of Bd infection; across the remaining 12 Bd-positive sites, neither infection prevalence nor intensity varied systematically. We found a more complicated pattern of Bd prevalence than anticipated. Early season samples showed no trend associated with increasing temperature and precipitation and decreasing (more southerly) latitudes; while in late season samples, the proportion of infected individuals decreased with increasing temperature and precipitation and decreasing latitudes. A similar pattern held for the east–west gradient, with the highest prevalence associated with more easterly/recently warmer sites in the early season then shifting to more westerly/recently cooler sites in the later season. Bd intensity across bases and sampling periods was comparatively low. Some of the trends in our data have been seen in previous studies, and our results offer further continental-level Bd sampling over which more concentrated local sampling efforts can be overlaid.     

Seasonal variations in moisture use in a piñon–juniper woodland

In water-limited environments of the intermountain region of North America, summer precipitation may play a role in the structure and function of aridland communities and ecosystems. This study examined the potential reliance on summer precipitation of two widespread, coexisting woody species in the southwestern United States, Pinus edulis Englmn. (Colorado piñon) and Juniperus osteosperma (Torr) Little (Utah juniper). The current distributions of P. edulis and J. osteosperma are highly suggestive of different dependencies on summer rainfall. We hypothesized that P. edulis was dependent on summer precipitation, utilizing summer precipitation even during extremely dry summers, whereas J. osteosperma was not dependent, using summer precipitation only when amounts were above some minimum threshold. Using sap flux and stable isotopic methods to assess seasonal water sources and water use efficiency, we examined the response of these two species to seasonal variations in moisture at a site located near the northern limits of the North American monsoon. Both sap flux and isotopic results indicated that P. edulis was responsive to summer rain, while J. osteosperma was not. Following summer rain events, sap flux density increased in P. edulis for several days, but not in J. osteosperma. Isotopic evidence indicated that P. edulis took up summer-derived moisture to a greater extent than J. osteosperma. Values of the natural abundance stable isotope ratio of carbon of leaf soluble carbohydrates increased over the summer for P. edulis, indicative of assimilation at higher water use efficiency, but were invariant for J. osteosperma. Our results supported the hypothesis that P. edulis and J. osteosperma are differentially sensitive to summer precipitation and are discussed in the light of potential changes in the seasonality of precipitation associated with climate change.     

Daily activity rhythm of desert omni-seasonal Tenebrionid beetles, <Emphasis Type="Italic">Trigonoscelis gigas</Emphasis> and <Emphasis Type="Italic">T. sublaevicollis</Emphasis> (Coleoptera,Tenebrionidae) in constant darkness and under alternating 1-hour pulses of light and darkness

In the Karakum Desert (Turkmenistan) the beetles Trigonoscelis gigas are only active in the morning and evening while T. sublaevicollis are strictly nocturnal, regardless of the season and weather. The daily activity rhythm of T. gigas and T. sublaevicollis was studied in the laboratory according to the following pattern: 5 days under a light-darkness cycle of 15: 9 h (LD 15: 9), then 10 days in constant darkness (DD), and then 10 more days under alternating 1-h pulses of light and darkness (LD 1: 1). The temperature was 25°C in all the modes. At LD 15: 9, beetles of both species maintained a 24-h period and a natural pattern of the activity rhythm. In DD, the circadian rhythm ran with a period of 23.5 ± 0.3 h (n = 40) in T. gigas and 23.6 ± 0.4 h (n = 40) in T. sublaevicollis. At DD, the morning and evening activity peaks of T. gigas merged to form a rhythm with only one peak. Under LD 1: 1, both T. gigas and T. sublaevicollis recovered a 24-h period of the rhythm, while the rhythm of T. gigas regained the two-peak structure. Our research confirmed the assumption of Tshernyshev (1980) about the 24-h period of the free-running endogenous rhythm and the distorting effect of constant conditions on this rhythm.     

Transpiration of trees in a cool temperate forest on Mt. Aso,Japan: comparison of model simulation and measurements

In the large caldera of Mt. Aso, Japan, artificial grasslands were converted into forests of different species due to the decline of the livestock industry in this region. These changes in species composition are thought to have changed not only the transpiration rates (E), but also the responses in E to variations in environmental conditions. For three introduced forest types, we monitored E using sap flux sensors and computed E with a multilayer model parameterized by independently obtained leaf-scale ecophysiological traits. Modeled E replicated the time series of measured E reasonably well, but did not reproduce a decrease in E lasting 20 days after a short rainless period in conifer plantation. Mean leaf-scale stomatal conductance of two deciduous broadleaved tree species was as low as that of trees under dry conditions in other studies, possibly an adaptation for the avoidance of excessive E during rainless periods. These results suggest that land use change influenced E and its response to the rainfall patterns of the region and that drought plays an important role in influencing species-specific E characteristics in this rainy region. The multilayer model in combination with sap flux measurements was found to be a useful tool not only for the extrapolation of E, but also for the detection of the unexpected events, as long as the measured parameter values capture the species-specific seasonality in leaf ecophysiological traits.     

Genome-wide identification and evolution of <Emphasis Type="Italic">TC1</Emphasis>/<Emphasis Type="Italic">Mariner</Emphasis> in the silkworm (<Emphasis Type="Italic">Bombyx mori</Emphasis>) genome

TC1/Mariner transposons belong to class II transposable elements (TEs) that use DNA-mediated “cut and paste” mechanism to transpose, and they have been identified in almost all organisms. Although silkworm (Bombyx mori) has a large amount of TC1/Mariner elements, the genome wide information of this superfamily in the silkworm is unknown. In this study, we have identified 2670 TC1/Mariner (Bmmar) elements in the silkworm genome. All the TEs were classified into 22 families by means of fgclust, a tool of repetitive sequence classification, seven of which was first reported in this study. Phylogenetic and structure analyses based on the catalytic domain (DDxD/E) of transposase sequences indicated that all members of TC1/Mariner were grouped into five subgroups: Mariner, Tc1, maT, DD40D and DD41D/E. Of these five subgroups, maT rather than Mariner possessed most members of TC1/Mariner (51.23%) in the silkworm genome. In particular, phylogenetic analysis and structure analysis revealed that Bmmar15 (DD40D) formed a new basal subgroup of TC1/Mariner element in insects, which was referred to as bmori. Furthermore, we concluded that DD40D appeared to intermediate between mariner and Tc1. Finally, we estimated the insertion time for each copy of TC1/Mariner in the silkworm and found that most of members were dramatically amplified during a period from 0 to 1 mya. Moreover, the detailed functional data analysis showed that Bmmar1, Bmmar6 and Bmmar9 had EST evidence and intact transposases. These implied that TC1/Mariner might have potential transpositional activity. In conclusion, this study provides some new insights into the landscape, origin and evolution of TC1/Mariner in the insect genomes.     

Types of the daily course of transpiration rate in seedlings of forest trees

Types of the daily course of transpiration rate were studied in two-year old seedlings ofPinus silvestris L.,Picea excelsa L.,Larix decidua L.,Tilia cordata Mill., andAlnus glu-tinosa (L.) Gaertn. The curves illustrating the daily development of transpiration rate (Figs. 3 - 8) may be grouped in two types, showing a midday maximum (one-peak curves) and a midday depression (two-peak curves). Unlike herbaceous plants, the seedlings ofPinus silvestris L. were found to show, during the night-time, lower but not negligible values for the rate of transpiration (see Figs. 3 and 8). The following times are considered most suitable in determining the rate of transpiration for both herbs and woody species during the daylight: 09.0, 12.0, 14.0, and 17.0 hours. For the forest species seedlings further times are suitable for the night-time, as follows: 23.0, 01.0, and 06.0 hours. The rate of transpiration in the seedlings of Pinus silvestris attained very low levels at 3 and between 6 and 8 a.m. and between 6 and 8 p.m. (see Figs 3 and 8).     

Nitrogen-induced variations in leaf gas exchange of spring triticale under field conditions

Nitrogen (N) is the key factor limiting photosynthetic processes and crop yield. Little is known about the response of leaf gas exchange of spring triticale (Triticosecale Wittm.) to N supply. The effect of N fertilizers on different gas exchange variables, i.e., photosynthetic rate (A), transpiration rate (E), stomatal conductance (g _s), instantaneous water use efficiency (WUE) and maximum quantum yield of photosystem II (PSII) (F _v/F _m), chlorophyll index (SPAD, soil–plant analysis development), and the relationship of these variables with yield were studied in spring triticale grown under field conditions. Six treatments of N—0, 90, 180, 90 + 30, 90 + 30 + 30 kg ha^?1 (applied as ammonium nitrate, AN) and one treatment of N 90 + 30 + 30 kg ha^?1 (applied as urea ammonium nitrate solution, UAN) were compared. The analysis of variance showed that throughout the triticale growing season, N fertilization had significant effects on A, WUE, g _s and SPAD. On average, N fertilizer application increased A values by 14–70%. E and F _v/F _m values were not influenced by N fertilization levels. The effect of growth stage and year on gas exchange variables and F _v/F _m and SPAD was found to be significant. At different growth stages, A values varied and maximum ones were reached at BBCH 31–33 (decimal code system of growth stages) and BBCH 59. With aging, values of A decreased independently of N fertilization level. The gas exchange variables were equally affected by both fertilizer forms. The interplay among grain yield, leaf gas exchange variables, F _v/F _m and SPAD of spring triticale was estimated. The statistical analysis showed that grain yield positively and significantly correlated with A and SPAD values throughout the growing season.     

Green roof <Emphasis Type="Italic">Petunia</Emphasis>, <Emphasis Type="Italic">Ageratum</Emphasis>, and <Emphasis Type="Italic">Mentha</Emphasis> responses to water stress,seaweeds, and trinexapac-ethyl treatments

The availability of sufficient irrigation water and the development of drought-tolerant species are challenging factors in the design and maintenance of green roofs in modern cities. Green roof plants of Petunia hybrid Headliner^® Red Star, Ageratum hybrid Artist^® blue, and Mentha spicata L. grown in a simulated green roof pot system under controlled greenhouse conditions. The plants were watered every 2 or 6 days (2DWI/6DWI) for 8 weeks accompanied by either a 6-day treatment of seaweed extracts of Ascophyllum nodosum as a soil drench or foliar spray, or two concentrations of trinexapac-ethyl (TE) biweekly sprays. Following treatments, leaf number, leaf area, dry weights, plant height, stomatal conductanse, photosynthetic and transpiration rates and leaf water potential and relative water content were determined in two seasons during 2016 and 2017. The prolonged irrigation intervals reduced plant growth as revealed by morphological and physiological parameters. The application of SWE as drench treatment improved Petunia and Ageratum plant vegetative growth, stomatal conductance, photosynthetic and transpiration rates and leaf water potential and relative water content during prolonged irrigation intervals. TE increased the vegetative growth as well as the physiological performance of Ageratum plants. However, neither SWE nor TE treatments improved the performance of Mentha plants under prolonged irrigation intervals. It was suggested that improved photosynthetic rates were stimulated by enhanced stomatal conductance leading to improved leaf water potential as well as increased relative water content during prolonged irrigation conditions.     

Changes in photosynthesis of alpine plant <Emphasis Type="Italic">Saussurea superba</Emphasis> during leaf expansion

The native alpine plant Saussurea superba is widely distributed in Qinghai–Tibetan Plateau regions. The leaves of S. superba grow in whorled rosettes, and are horizontally oriented to maximize sunlight exposure. Experiments were conducted in an alpine Kobresia humilis meadow near Haibei Alpine Meadow Ecosystem Research Station (37°29′–37°45′N, 101°12′–101°33′E; alt. 3200 m). Leaf growth, photosynthetic pigments and chlorophyll fluorescence parameters were measured in expanding leaves of S. superba. The results indicate that leaf area increased progressively from inner younger leaves to outside fully expanded ones, and then slightly decreased in nearly senescent leaves, due to early unfavorable environmental conditions, deviating from the ordinary growth pattern. The specific leaf area decreased before leaves were fully expanded, and the leaf thickness was largest in mature leaves. There were no significant changes in the content of chlorophylls (Chl) and carotenoids (Car), but the ratios of Chl a/b and Car/Chl declined after full expansion of the leaves. The variation of Chl a/b coincided well with changes in photochemical quenching (q _P) and the fraction of open PSII reaction centers (q _L). The maximum quantum efficiency of PSII photochemistry after 5 min dark relaxation (F _(v)/F _(m)) continuously increased from younger leaves to fully mature leaves, suggesting that mature leaves could recover more quickly from photoinhibition than younger leaves. The light-harvesting capacity was relatively steady during leaf expansion, as indicated by the maximum quantum efficiency of open PSII centers (\(F_{\text{v}}^{{\prime }}\)/\(F_{\text{m}}^{{\prime }}\)). UV-absorbing compounds could effectively screen harmful solar radiation, and are a main protection way on the photosynthetic apparatus. The decline of q _P and q _L during maturation, together with limitation of quantum efficiency of PSII reaction centers (L _(PFD)), shows a decrease of oxidation state of Q_A in PSII reaction centers under natural sunlight. Furthermore, light-induced (Φ _NPQ) and non-light-induced quenching (Φ _NO) were consistent with variation of L _(PFD). It is concluded that the leaves of S. superba could be classified into four functional groups: young, fully expanded, mature, and senescent. Quick recovery from photoinhibition was correlated with protection by screening pigments, and high level of light energy trapping was correlated with preservation of photosynthetic pigments. Increasing of Φ _NPQ and Φ _NO during leaves maturation indicates that both thermal dissipation of excessive excitation energy in safety and potential threat to photosynthetic apparatus were strengthened due to the declination of q _P and q _L, and enhancement of L _(PFD).     

Interannual variation in rainfall,drought stress and seedling mortality may mediate monodominance in tropical flooded forests

Flood tolerance is commonly regarded as the main factor explaining low diversity and monodominance in tropical swamps. In this study we examined seedling mortality in relation to seasonality, i.e., flooding versus drought, of the dominant tree species (Prioria copaifera), and three associated species (Pterocarpus officinalis, Carapa guianensis and Pentaclethra macroloba), in seasonally flooded forests (SFF) in Darien, Panama. Seedling mortality differed among species, years and seasons. Prioria seedlings experienced the lowest overall mortality, and after 3 years many more Prioria seedlings remained alive than those of any of the associated species. In general, within species, larger seedlings had greater survival. Seed size, which can vary by close to 2 orders of magnitude in Prioria, had a confounding effect with that of topography. Large-seeded Prioria seedlings experienced 1.5 times greater mortality than small-seeded seedlings, as large-seeded Prioria seedlings were more likely to be located in depressions. This finding suggests that seed size, plant size and topography are important in understanding SFF regeneration. For all species, seedling mortality was consistently greater during the dry season than during flooding. For Prioria, dry season seedling mortality was correlated with drought stress, that is, high mortality during the long El Niño dry season of 1998 and the normal dry season of 2000, but very low dry season mortality during the mild dry season of 1999. Prioria’s ability to dominate in seasonally flooded forest of Central America is partly explained by its low drought-related mortality in comparison to associated species.     

Comparative study of daytime and nighttime sap flow of <Emphasis Type="Italic">Populus euphratica</Emphasis>

In order to quantify and characterize the variance in desert riparian forest tree sap flow, we measured the sap flow from Populus euphratica and compared the daytime and nighttime patterns and responses to environmental variables. Results showed that daytime sap flow velocity was significantly higher (P?<?0.05). Daytime and nighttime mean sap flow velocities were 7.65 and 4.01 cm h^?1 in spring, 21.38 and 9.60 cm h^?1 in summer, and 11.04 and 5.21 cm h^?1 in autumn, respectively. Moreover, results indicated that the stoma remained partially open (15% minimum) throughout the night, providing sufficient evidence for the existance of nighttime transpiration. The vapor pressure deficit (VPD), stomatal conductance (Cs), photosynthetically active radiation (PAR), air temperature (Ta), wind speed (WS), and soil moisture (θ) all had significant positive effects on P. euphratica sap flow velocity (P?<?0.05). Furthermore, the relationship between daytime sap flow velocity and VPD showed clockwise hysteresis, while the relationship between nighttime sap flow velocity and VPD showed counter-clockwise hysteresis. It was evident that PAR and VPD were the key factors impacting daytime sap flow velocity, while Cs and θ were the key factors impacting nighttime sap flow velocity. Furthermore, linear regression results showed that daytime sap flow had a significant positive effect on nighttime sap flow throughout the growing season (P?<?0.05).