热带雨林三种树苗叶片光合机构对光强的适应

对生长在不同光强(自然日光的8％,25％,50％)下西双版纳热带雨林3种木本植物团花(Anthocephalus chinensis)、玉蕊(Barringtonia pendala)和藤黄(Garrcinia hanburyi)幼苗光合机构的研究表明,随着生长光强的升高,植物叶片的光饱和点、补偿点、净光合速率和非光化学淬灭系数(NPQ)升高,而表现量子效率(AQY)、有效光化学量子产量(Fv／Fm)、光化学淬灭系数(qP)下降．在抗氧化系统中,超氧化物歧化酶(SOD)、抗坏血酸过氧化酶(APX)活性随着光强的升高而升高,而过氢化物酶(CAT)活性与生长光强的变化不一致．抗坏血酸(AsA)含量随着光强的升高而急剧上升。最能反映PFD的变化．可以认为,除与叶黄素循环有关的热耗散增大之外,植物叶片抗氧化系统的加强也是响应强光的一种保护措施．     

Time-course of photosynthetic induction in four tropical woody species grown in contrasting irradiance habitats

We investigated the photosynthetic induction time-course in species of different ecological groups grown in contrasting forest irradiance environments, gap and understorey, exposed to different darkness times in order to verify the plant capacity to exploit irradiance heterogeneity. Photosynthetic induction was studied in leaves of Bauhinia forficata and Guazuma ulmifolia (early succession species, ES), and Esenbeckia leiocarpa and Hymenaea courbaril (late succession species, LS). T₅₀ and T₉₀ (time estimates to attain 50 and 90 % of maximum net photosynthetic rate, respectively) varied according to the time of previous exposure to darkness and growth irradiance. In both darkness times of 10 and 30 min, T₅₀ was lower in the LS-than ES-species. These results, jointly with significant higher induction state of the leaves after 10 min of darkness, suggest that the LS-species has a higher potential to sunfleck utilization compared to ES-species, both grown in the understorey. After 10 and 30 min of darkness the differences between ecological groups were not clearly detected in the gap for T₅₀ and T₉₀, indicating that eco-physiological characteristics of each ecological group did not influence the induction time of the species evaluated herein. Thus the capacity to show phenotypic plasticity is not exclusive to an ecological group, but it is rather a more intrinsic feature related to the differential capacity of individuals.     

Comparison of temperate and tropical rainforest tree species: photosynthetic responses to growth temperature

Little is known about the differences in physiology between temperate and tropical trees. Australian rainforests extend from tropical climates in the north to temperate climates in the south over a span of 33° latitude. Therefore, they provide an opportunity to investigate differences in the physiology of temperate and tropical trees within the same vegetation type. This study investigated how the response of net photosynthesis to growth temperature differed between Australian temperate and tropical rainforest trees and how this correlated with differences in their climates. The temperate species showed their maximum rate of net photosynthesis at lower growth temperatures than the tropical species. However, the temperate species showed at least 80% of maximum net photosynthesis over a 12-16°C span of growth temperature, compared with a span of 9-11°C shown by the tropical species. The tropical species showed both larger reductions in maximum net photosynthesis at low growth temperatures and larger reductions in the optimum instantaneous temperature for net photosynthesis with decreasing growth temperature than the temperate species. The ability of the temperate species to maintain maximum net photosynthesis over a greater span of growth temperatures than the tropical species is consistent with the greater seasonal and day-to-day variation in temperature of the temperate climate compared with the tropical climate.     

Resource availability and growth responses to defoliation in seedlings of three early-successional,tropical, woody species

A growth experiment was conducted using seedlings of three early-successional, tropical, woody species:Dillenia suffruticosa (Dilleniaceae),Macaranga heynei (Euphorbiaceae) andTrema tomentosa (Ulmaceae). These species are characteristic of different positions along a soil fertility gradient in Singapore, withD. suffruticosa being the least andT. tomentosa the most demanding of high nutrient availability. The seedlings were grown in vermiculite at either low or high nutrient availabilities supplied by watering with different concentrations of a commercial plant food. Half the seedlings were subjected to a 50% defoliation at the start of the experiment by cutting off the distal half of each leaf. After 9 weeks the plants were harvested.Macaranga heynei andT. tomentosa seedlings showed no significant difference in parameters of growth such as total dry weight and total leaf area between the defoliated and control seedlings. The seedlings compensated completely for the loss of leaf area.Dillenia suffruticosa did show significant reductions in growth in some parameters due to defoliation, and these were more pronounced under the high nutrient treatment. These findings support the hypothesis that plants characteristic of resource-rich sites can readily recover from herbivory through fast growth, probably associated with a rapid turnover of leaves, whereas species of resource-poor habitats cannot easily replace losses due to herbivory and are adversely effected by defoliation.     

The capacity to emit isoprene differentiates the photosynthetic temperature responses of tropical plant species

Experimental research shows that isoprene emission by plants can improve photosynthetic performance at high temperatures. But whether species that emit isoprene have higher thermal limits than non‐emitting species remains largely untested. Tropical plants are adapted to narrow temperature ranges and global warming could result in significant ecosystem restructuring due to small variations in species' thermal tolerances. We compared photosynthetic temperature responses of 26 co‐occurring tropical tree and liana species to test whether isoprene‐emitting species are more tolerant to high temperatures. We classified species as isoprene emitters versus non‐emitters based on published datasets. Maximum temperatures for net photosynthesis were ~1.8°C higher for isoprene‐emitting species than for non‐emitters, and thermal response curves were 24% wider; differences in optimum temperatures (T_opt) or photosynthetic rates at T_opt were not significant. Modelling the carbon cost of isoprene emission, we show that even strong emission rates cause little reduction in the net carbon assimilation advantage over non‐emitters at supraoptimal temperatures. Isoprene emissions may alleviate biochemical limitations, which together with stomatal conductance, co‐limit photosynthesis above T_opt. Our findings provide evidence that isoprene emission may be an adaptation to warmer thermal niches, and that emitting species may fare better under global warming than co‐occurring non‐emitting species.     

Response of native Hawaiian woody species to lava-ignited wildfires in tropical forests and shrublands

Wildfires are rare in the disturbance history of Hawaiian forests but may increase in prevalence due to invasive species and global climate change. We documented survival rates and adaptations facilitating persistence of native woody species following 2002–2003 wildfires in Hawaii Volcanoes National Park, Hawaii. Fires occurred during an El Niño drought and were ignited by lava flows. They burned across an environmental gradient occupied by two drier shrub-dominated communities and three mesic/wet Metrosideros forest communities. All the 19 native tree, shrub, and tree fern species demonstrated some capacity of postfire persistence. While greater than 95% of the dominant Metrosideros trees were top-killed, more than half survived fires via basal sprouting. Metrosideros trees with diameters >20 cm sprouted in lower percentages than smaller trees. At least 17 of 29 native woody species colonized the postfire environment via seedling establishment. Although the native biota possess adaptations facilitating persistence following wildfire, the presence of highly competitive invasive plants and ungulates will likely alter postfire succession.     

Growth responses of a woody species to clipping and goat saliva

Studies on the role of mammalian herbivore saliva in plant–animal interactions have mostly focused on graminoid species and bovine saliva. A trial was performed in Botswana with clipping treatments to simulate browsing of shoots and the application of goat saliva on the woody species Combretum apiculatum Sonder (Combretaceae). Treatments were performed during early growing season while shoot growth was rapid, and responses of trees were recorded later in the same season. Clipped shoots with saliva had significantly enhanced shoot growth (tripled in length) and leaf production (2.7 times more leaves) compared to clipped shoots without saliva. However, unclipped shoots still grew more than clipped shoots, with or without saliva treatment.     

Phosphorus recycling in photorespiration maintains high photosynthetic capacity in woody species

Leaf photosynthetic CO₂ responses can provide insight into how major nutrients, such as phosphorus (P), constrain leaf CO₂ assimilation rates (A_net). However, triose‐phosphate limitations are rarely employed in the classic photosynthesis model and it is uncertain as to what extent these limitations occur in field situations. In contrast to predictions from biochemical theory of photosynthesis, we found consistent evidence in the field of lower A_net in high [CO₂] and low [O₂] than at ambient [O₂]. For 10 species of trees and shrubs across a range of soil P availability in Australia, none of them showed a positive response of A_net at saturating [CO₂] (i.e. A_max) to 2 kPa O₂. Three species showed >20% reductions in A_max in low [O₂], a phenomenon potentially explained by orthophosphate (P_i) savings during photorespiration. These species, with largest photosynthetic capacity and P_i > 2 mmol P m^?2, rely the most on additional P_i made available from photorespiration rather than species growing in P‐impoverished soils. The results suggest that rarely used adjustments to a biochemical photosynthesis model are useful for predicting A_max and give insight into the biochemical limitations of photosynthesis rates at a range of leaf P concentrations. Phosphate limitations to photosynthetic capacity are likely more common in the field than previously considered.     

Physiological dormancy in seeds of tropical montane woody species in Hawai`i

Worldwide, there is relatively little information on seed dormancy and germination of tropical montane species. Our aim was to help fill this knowledge gap by conducting seed dormancy/germination studies on woody species from this vegetation zone in Hawai`i. All species had water-permeable seeds with a fully developed embryo. Seeds of 29 species (23 genera) were incubated in light/dark at 15/6, 20/10 and 25/15°C and germination monitored at 2-week intervals for 16–128 weeks. Seeds of Chenopodium oahuense, Dubautia menziesii and Silene lanceolata were non-dormant (ND) and those of 26 other species had physiological dormancy (PD); 10 of the 26 species had conditional PD. The optimum germination temperature regime(s) was (were) 25/15°C, 17 species; 25/10 and 20/10°C, 2; 20/10°C, 6; 20/10 and 15/6°C, 2; and 15/6°C, 2. Worldwide, PD in the woody genera included in our study is more common than ND. In addition to its contribution to the world biogeography of seed dormancy/germination, this study will be useful to conservation biologists who need to germinate seeds of tropical montane species.     

Phenology of woody species in tropical coastal vegetation, northeastern Brazil

The study was carried out in the Private Nature Reservation Nossa Senhora do Outeiro de Maracaípe, located along the southern coast of Pernambuco state, in the Nossa Senhora do Ó District (08°31′48″S and 35°01′05″W), Ipojuca municipality, northeastern Brazil. The reserve has 76.20 ha of tropical coastal vegetation (Restinga forest). The aims were to determine the existence of seasonal phenological pattern of woody species as a function of rainfall. During the study period, the rainfall was 26.8 mm in the driest month (November 2003) and 538.9 in the wettest (June 2004). Observations on flowering, fruiting, leaf fall, and leaf flushing were recorded monthly, during 16 months (April 2003 to July 2004). All species with a ground level perimeter >10 cm and represented by at least three individuals, were selected and tagged. A total of 51 species represented by 156 individuals were recorded. Leaf flushing and leaf fall did not have seasonal variation and the species continued to gain and loose leaves during the dry (August to February) and rainy (March to July) seasons. Flowering, when evaluated by the Fournier's percentage, varied between 1.9% and 20.2%, with maximum intensity in December 2003 (16.4%) and January 2004 (20.2%). Likewise, fruiting varied between 3.8% and 21.4% with the highest percentages in February (17.2%) and March (21.4%) 2004. The analysis comparing reproductive phenological patterns with monthly rainfall did not show a significant correlation, which may suggest investigations concerning other factors, including biotic ones, as pollination and/or dispersal modes, which can be influencing reproductive events of plants in the studied Restinga forest.     

Contrasting leaf phenology of woody species of dry tropical forest

We studied selected leaf traits [leaf area (LA), leaf water content (LWC), leaf fresh weight (LFW), leaf dry weight (LDW), specific leaf area (SLA) and chlorophyll content] of eight woody species (Shorea robusta, Buchanania lanzan, Diospyros melanoxylon, Lagerstroemia parviflora, Lannea coromandelica, Terminalia tomentosa, Holarrhena antidysenterica and Lantana camara) dominant at four sites in a dry tropical deciduous forest over complete two annual cycles (2008–2010). Our results showed that leaf traits varied across species (1.7–11.5 fold), months (1.2–1.5 fold) and sites (1.1–1.3 fold). However, leaf traits showed smaller variation between sites than between species. Leaf lifespan varied from 7 months (L. coromandelica) to 12 months (S. robusta). On the same sites, species differed in the length of deciduous period. The maximum LA, LDW, LFW and LWC were recorded for the semi-evergreen species, SLA for long-deciduous species and chlorophyll content for short-deciduous species, respectively. The coefficient of variation was maximum for LDW and minimum for chlorophyll content. Among the eight woody species, T. tomentosa exhibited the greatest LA, LDW, LFW and LWC. LA, LWC, LFW, LDW, SLA, LD, SD, MD & SE confirm.     

Growth responses of tropical forage plant species to vesicular-arbuscular mycorrhizae

Summary Growth and mineral uptake of twenty-four tropical forage legumes and grasses were compared under glasshouse conditions in a sterile low P oxisol, one part inoculated and the other not inoculated with mycorrhizal fungi. Shoot and root dry weights and total uptake of P, N, K, Ca, and Mg of all the test plants were significantly increased by mycorrhizal inoculation. Mycorrhizal inoculation, with few exceptions, decreased the root/shoot ratio. Non-mycorrhizal plants contained always lower quantities of mineral elements than mycorrhizal plants. Plant species showed differences in percentage mycorrhizal root length and there was no correlation between percentage mycorrhizal infection and plant growth parameters. A great variation in dependence on mycorrhiza was observed among forage species. Total uptake of all elements by non-mycorrhizal legumes and uptake of P, N and K by non-mycorrhizal grasses correlated inversely with mycorrhizal dependency. Mycorrhizal plants of all species used significantly greater quantities of soil P than the nonmycorrhizal plants. Utilization of soil P by non-mycorrhizal plants was correlated inversely with mycorrhizal dependency.     

Growth and photosynthetic responses of four landscape shrub species to elevated ozone

Attention should be paid to ozone (O₃) sensitivity of greening plant since ground-level O₃ concentrations are increasing especially in urban and suburban area. We studied the ecophysiological responses to elevated O₃ of four shrub species [Euonymus bungeanus Maxim. (EB), Photinia × fraseri (PF), Chionanthus retusus Lindl. & Paxt. (CR) and Cornus alba L. (CA)], which are often used for garden greening in China. Saplings of those species were exposed to high O₃ concentration (70 nmol mol⁻¹, 7 h d⁻¹ for 65 d) in open-top growth chambers. Responses to O₃ were assessed by gas exchanges, chlorophyll (Chl) fluorescence and dry mass. We found that elevated O₃ significantly decreased lightsaturated net photosynthetic rate (P _Nsat), transpiration rate (E) and stomatal conductance (g _s). The ratio of intercellular CO₂ to ambient CO₂ concentration (C _i/C _a) did not reduce under O₃ fumigation which suggested that the O₃-induced depressions of P _Nsat under O₃ fumigation were probably due to limitation of mesophyll processes rather than stomatal limitation. High O₃ exposure also significantly depressed the maximum efficiency of photosystem II (PSII) photochemistry in the dark-adapted state (F_v/F_m) which meant the O3-induced photoinhibition. Both root dry mass and root/shoot ratios were significantly decreased under ozone fumigation, but the total mass was unchanged. The responses of gas exchange such as P _Nsat in these four shrubs to O₃ exposure were species-specific. Highest loss of P _Nsat was observed in EB (−49.6%), while the CR had the lowest loss (−36.5%). Moreover, the O₃-exposed CR showed similar g _s as CF, reflecting that its O₃ flux might be unchanged under elevated O₃ environment. Ozone drastically decreased actual quantum yield of PSII (Φ_PSII) and electron transport rate (ETR) in EB while increased Φ_PSII and ETR in CR. Furthermore, the relative losses in P _Nsat positively correlated with the relative decreases in Φ_PSII and ETR which indicated that the impairment of photosynthesis was probably affected by the light reaction process. The light reaction of EB was impaired most seriously but that of CR was not damaged. All results indicated that EB was probably the most sensitive shrub species to O₃ while CR the most tolerant one. Therefore, CR might be an ideal choice for greening in ozone-polluted areas.     

Stomatal versus biochemical limitations to dynamic photosynthetic performance in four tropical rainforest shrub species

Photosynthetic performance under dynamic light regimes was assessed in four different species of tropical shrubs from the family Rubiaceae via field gas exchange measurements conducted on Barro Colorado Island, Panamá. Rates of photosynthetic induction and induction loss were assessed throughout the day in both the wet and dry seasons in order to determine the relative roles of stomata and biochemistry in limiting photosynthetic performance under transient light conditions. A high degree of coordination was observed between stomatal conductance and biochemical capacity for CO₂ assimilation during induction. Rates of biochemical and overall photosynthetic induction sharply decreased when initial stomatal conductance fell below a narrow range of critical values. Time of day or season did not affect rates of biochemical deactivation upon shading, but did influence stomatal closure, which often exerted a significant influence over induction loss in the darkness. In measurements of total assimilation due to a 60-s light pulse, both biochemical activity and stomatal conductance were linearly related to total CO₂ uptake. Only during the mornings of the wet season was stomatal conductance consistently high enough to be non-limiting to dynamic photosynthetic performance. At all other times, stomatal behavior exercised significant influence over induction times, photosynthetic induction loss, and total CO₂ uptake from 60-s light pulses. Received: 17 March 1999 / Accepted: 26 October 1999     

Leaf and photosynthetic characteristics of pioneer and forest species in tropical montane habitats

Gas exchange and chlorophyll a fluorescence measurements of expanding and adult leaves of four plant species were compared under field conditions. The pioneer species (PS) tended to have thinner leaves with lower nitrogen content and higher stomatal density compared to forest species (FS). Expanding leaves featured lower photosynthetic pigment contents and gas exchange capacity than adult leaves consistent with an immature photosynthetic apparatus. At the time of maximum irradiance, sun-exposed leaves of both PS and FS showed alteration of initial, variable, and maximum fluorescence as well as their ratios indicating photoinhibition. However, leaves recovered to some extent at predawn, suggesting the activation of photoprotective mechanisms. Sun-exposed leaves had comparable responses to high irradiance.