Relative growth rate and biomass allocation in ten woody species with different leaf longevity using phylogenetic independent contrasts (PICs)

In this study, we compare the relative growth rate (RGR) and biomass allocation of 10 woody species (5 deciduous and 5 evergreen) from the Mediterranean region using phylogenetic independent contrasts (PICs) to test if these two functional groups differ in these traits. In general, the results were similar when using PICs or without taking into account phylogenetic relations. Deciduous species had a higher RGR than evergreen species, due to the higher net assimilation rate (NAR). Deciduous species had a higher specific leaf area (SLA) but a lower leaf mass ratio (LMR), resulting in a similar LAR for deciduous and evergreen species (LAR = SLA x LMR). In some cases, the use of PICs revealed patterns that would not have appeared if phylogeny had been overlooked. For example, there was no significant correlation between RGR and final dry mass (after 4 months of growth) but PICs revealed that there was a positive relation between these two variables in all deciduous-evergreen pairs. In general, RGR decreased with time and this temporal variation was due primarily to NAR variations (r = 0.79, p < 0.01), and also to variations in LAR (r = 0.69, p < 0.05). Considering the phylogeny, the only variable constantly different for all deciduous-evergreen pairs was SLA. This result, and the fact that SLA was the best correlated variable with RGR (r = 0.81, p < 0.01), reinforce the value of SLA as a variable closely associated to growth and to the functional groups (deciduous vs. evergreen).     

Seasonal changes in soil arthropod abundance in the dry evergreen forest of north-east Thailand,with special reference to collembolan communities

A soil arthropod community was studied in a dry evergreen forest over a 3-year period from May 1998 to April 2001. Population abundance, species composition, and community structure were investigated over the 3-year study period. The soil arthropods consisted of Acari (75.38%), Collembola (16.11%), and others (8.51%), and their abundances showed a clear difference between the rainy and dry seasons. Population abundance of Collembola and Acari were low during drought conditions. The humidity was the most important factor determining distribution, abundance, and survival of soil Collembola in this tropical forest. High predation and low accumulation of organic matter caused low population abundance of Collembola in the tropical habitat. The collembolan community was dominated by a few dominant species over the study period. The pattern of seasonal changes in numbers of Collembola was similar over the 3-year study period. The species composition of the collembolan community was constant and persistent throughout a 3-year study period. Thus, the collembolan community showed constancy in its species composition with seasonal variability over the 3-year study period.     

A botanical inventory of a tropical seasonal forest in Khao Yai National Park,Thailand: implications for fruit–frugivore interactions

The diversity of plants in tropical forests makes dietary studies of frugivores difficult. This paper provides a botanical inventory of a tropical seasonal forest community in Khao Yai National Park, Thailand. The forest is valuable from a conservation perspective because it is one of the last remaining intact forests in northeastern Thailand, and is an important refuge for many animal and plant species. A 4-ha inventory plot measuring 200 × 200 m was established and all plants greater than or equal to 10 cm in diameter at breast height (dbh) were measured and permanently labeled. We found 1610 stems belonging to 105 species, 76 genera and 35 families, with a combined basal area of 142.5 m². The community was dominated by species of Lauraceae, Cornaceae, Euphorbiaceae, Meliaceae, and Elaeocarpaceae. About one-third of the plant species (40 spp.) identified in this study were vulnerable to extinction because they were mostly dispersed by large frugivores, which were intolerant of human impact. If they disappear, these forests may become dominated by plant species that are dispersed by abiotic means and species with small-seeded fruits.     

Functional role of anthocyanins in high-light winter leaves of the evergreen herb Galax urceolata

High-light leaves of the evergreen herb Galax urceolata exhibit a striking color change from green to red during winter months due to anthocyanin synthesis in outermost mesophyll cells. Here we investigate three possible functions of this color change. To test the hypothesis that anthocyanins function as light attenuators, maximum photosystem II efficiency (F(v)/F(m)) of red and green leaves was measured during and after exposure to wavelengths either strongly or poorly absorbed by anthocyanin. To determine whether anthocyanins elevate radical-scavenging capacity, antioxidant activity of red and green leaves was assessed using the alpha,alpha-diphenyl-beta-picrylhydrazyl assay. Nonstructural carbohydrate levels were analyzed to test the hypothesis that anthocyanins function as a carbon sink. Declines in F(v)/F(m) under white and green light were significantly greater for green than red leaves, but were comparable under red light. Anthocyanin content positively correlated with antioxidant activity. Although levels of anthocyanins did not appear to be related to nonstructural carbohydrate concentration, high levels of sugars may be necessary for their photo-induction. Results suggest that anthocyanins function as light attenuators and may also contribute to the antioxidant pool in winter leaves.     

Patterns and determinants of potential carbon gain in the C3 evergreen Yucca glauca (Liliaceae) in a C4 grassland

Yucca glauca is a C(3) evergreen rosette species locally common in the C(4)-dominated grasslands of the central Great Plains. Most congeners of Y. glauca are found in deserts, and Y. glauca's morphological similarities to desert species (steeply angled leaves, evergreen habit) may be critical to its success in grasslands. We hypothesized that the evergreen habit of Y. glauca, coupled with its ability to remain physiologically active at cool temperatures, would allow this species to gain a substantial portion of its annual carbon budget when the C(4) grasses are dormant. Leaf-level gas exchange was measured over an 18-mo period at Konza Prairie in northeast Kansas to assess the annual pattern of potential C gain. Two short-term experiments also were conducted in which nighttime temperatures were manipulated to assess the cold tolerance of this species. The annual pattern of C gain in Y. glauca was bimodal, with a spring productive period (maximum monthly photosynthetic rate = 21.1 ± 1.97 μmol·m·s) in March through June, a period of midseason photosynthetic depression, and a fall productive period in October (15.6 ± 1.25 μmol·m·s). The steeply angled leaves resulted in interception of photon flux density at levels above photosynthetic saturation throughout the year. Reduced photosynthetic rates in the summer may have been caused by low soil moisture, but temperature was strongly related (r = 0.37) to annual variations in photosynthesis, with nocturnal air temperatures below -5°C in the late fall and early spring, and high air temperatures (>32°C) in the summer, limiting gas exchange. Overall, 31% of the potential annual carbon gain in Y. glauca occurred outside the "frost-free" period (April-October) at Konza Prairie and 43% occurred when the dominant C(4) grasses were dormant. Future climates that include warmer minimum temperatures in the spring and fall may enhance the success of Y. glauca relative to the C(4) dominants in these grasslands.     

1980—1999年大兴安岭灌木、草本和地被物林火碳释放估算

应用排放因子法,对大兴安岭林区1980-1999年间主要森林类型中灌木、草本和地被物因森林火灾释放的碳量及主要含碳温室气体量进行了估算．结果表明：不同森林类型灌木、草本和地被物的排放因子不同,以杜香-兴安落叶松林的灌木、草本和地被物层CO2排放因子最大,为93．08％,樟子松林最小,为82．56％;樟子松林CO和CxHy排放因子最大,分别为10．25％和0．84％,杜香-兴安落叶松林最小,分别为6．55％和0．30％．结合灌木、草本和地被物层生物量和碳储量数据,得出20年间大兴安岭典型森林类型灌木、草本和地被物层因森林火灾释放的总碳量为6．56Tg,年平均0．33Tg,约占全国森林火灾碳释放量的11．55％～16．30％;直接释放的含碳温室气体22．03Tg,其中CO2的释放量占总释放量的85．20％,CO占总释放量的14．21％,CxHy占总释放量的0．59％．     

Seasonal changes in hydraulic conductance, xylem embolism and leaf area in Eucalyptus tetrodonta and Eucalyptus miniata saplings in a north Australian savanna

Eucalypt saplings in north Australian savannas commonly die back, sometimes to ground level, during the 5 months of the long dry season. Water potentials are lower in saplings than large trees during the dry season, and we hypothesized that low water potentials may lead to high levels of xylem embolism and consequent death of branches and whole shoots. As the dry season progressed, hydraulic conductance of terminal branches decreased by 50% in Eucalyptus tetrodonta but not in Eucalyptus miniata saplings. Hydraulic conductance per leaf area decreased seasonally by 34% in E. tetrodonta branches. These decreases may be associated with the loss of leaves recorded from E. tetrodonta but not E. miniata branches. We modelled the effect of sequential loss of parallel resistors, representing petioles on a branch. This showed there is a non-linear decrease in flow as basal resistors are lost, which can lead to a decrease in mean flow per resistor due to increased mean path-length. Thus the observed loss of basal leaves, together with xylem embolism, probably contributed to the seasonal loss of hydraulic conductance in E. tetrodonta saplings. Loss of hydraulic conductance due to xylem embolism was generally low ( < 15%) in both species, and the seasonal increase in embolism could not fully account for the decline in hydraulic conductance of E. tetrodonta branches. There was little evidence that branch and shoot death was caused by these levels of embolism. Developing an embolism vulnerability curve for species with long vessels is problematic and this issue is discussed.     

Nectary structure of Labiatae in relation to their nectar secretion and characteristics in a Mediterranean shrub community — Does flowering time matter?

We studied the interrelation between nectary structure (13 parameters), nectar characteristics (yield, chemical composition), and flower size of 11 Labiatae species in a Mediterranean shrub community near Athens, Greece. We also explored whether the above attributes are affected by the Mediterranean summer drought constraints. Our findings show that among all nectary parameters studied, nectary size and stomatal opening are the most important in (positively) shaping nectar secretion, nectary size being the most meaningful. Nectary structure is correlated to quantity of the nectar secreted, not its quality. Wide flowers bear wide nectaries with large stomatal openings, whereas deep flowers are not related to any nectary size. Corolla size (both length and width) and nectary stomatal opening decrease with flowering time. This applies also to nectary size, nectar volume and sugar content of the perennials (9 species). All above cases of time dependence show that there is a constraint effect of Mediterranean climate on floral and nectary structure, reflected also as a decrease in nectar secretion. Nectary structure in Labiatae is largely shaped by both phylogenetic and climate constraints. On the other hand, although nectar is largely influenced by nectary structure, it is to a large extent ecologically biased, implying that, in addition to phylogeny, there are many other ecological parameters interfering in its secretion such as time within the season, life history, and light requirements.     

Slow‐motion population dynamics in Mojave Desert perennial plants

Abstract. To investigate survivorship and regeneration in desert perennial plants, individual shrubs were mapped, measured and tagged on a nearly level 360 m² plot of diverse Mojave Desert vegetation in 1981, they were re‐mapped and measured 15 years later, in 1996. A large majority of the shrubs persisted between censuses. Modest birth (establishment) and death rates indicate that plants are replaced approximately every century, while the median longevity of several species is much longer. A 15‐yr intercensus interval, appropriate for most species (i.e. birth and death rates were measurable), is too short for several larger shrubs (including Larrea divaricata, Ephedra nevadensis, Yucca schidigera and the larger Opuntia spp.) in which virtually no births or deaths occurred and in which longevity must be extremely high. While individuals of most species grew over the 15‐yr interval, others did not, and some individuals shrank in size. In a number of species, individual growth rates were significantly reduced according to the number of neighbouring plants rooted 0.5–2.0 m distant. Even Larrea tridentata, one of the largest species, showed significant effects of growth rate reduction where crowded by allospecific plants, despite the generally much smaller sizes of these neighbours.     

A Study on the Classification of the Plant Functional Types Based on the Topographical Pattern of Plant Distribution

An idea of plant functional types (PFTs) classification is brought forward based on the topographical pattern of plants, and a case study at Daloling region, lying in the northern part of Chinese subtropical zone, is presented. By means of extensive field study of the mountain forests, the quantitative attributes of the major 55 evergreen broadleaved tree species in the communities located at various topographical positions were acquired. The detrended canerical corre spondence analysis (DCCA) method was used to analyze: 1) The correlationships among the habitat temperature, moisture and illumination conditions and the 6 topographical attributes as elevation, mountain aspect, slope shape, slope position, slope direction and slope gradient of the habitat. 2) The diverse patterns of 55 species on the multidimensional topographical gradients. The scores of ordination were then used for a two way indicator species analysis (TWINSPAN) to the species. According to the results of previous analyses, the 55 evergreen broadleaved tree species at Dalaoling were classified into 10 PFTs. A discussion about the validity and limits of this PFTs accessing approach were given in the end. 