1. Evergreen broad-leaved forests are widely distributed in eastern Asia with evergreen broad-leaved (EBL) and deciduous broad-leaved (DBL) tree species coexisting under the same climatic regime, ...raising questions as to the underlying mechanisms. Since EBL and DBL species differ in leaf life span, a key component of resource economic strategies, their coexistence might be attributed to regeneration niche partitioning across habitats varying in resource supply. 2. We investigated the effects of variation in insolation and topography on regeneration of EBL and DBL species in a subtropical EBL forest of eastern China after an ice storm that caused severe canopy disturbance. 3. Using a mixed-effects modelling framework and census data from 2011 to 2014 on 8,548 wild seedlings of 123 species, we quantified habitat preferences of EBL and DBL species during post-disturbance regeneration and how their survival and height relative growth rates varied among habitats. 4. The relative density of DBL seedlings (proportional to all seedlings) was greater in habitats with greater (canopy gaps) compared to habitats with lesser (understorey) insolation and increased with canopy gap size. However, DBL seedlings were not more frequent in higher (valleys) compared to lower (ridges) fertility habitats. Although DBL seedlings exhibited larger differences in growth between higher and lower resource habitats than EBL seedlings, their growth rates did not increase with canopy gap size. Seedlings of EBL species had high survival in all habitats, but larger DBL seedlings survived equally well on ridges. Consequently, the relative density of DBL seedlings declined in valleys, so that by 2014 it became more similar in valley and ridge habitats, whereas it remained higher in gaps than in the understorey, and especially in larger gaps. 5. Synthesis. Specialization on contrasting topographic habitats is considered the primary mechanism mediating coexistence between deciduous broad-leaved and evergreen broad-leaved species. Our results, however, suggest this may not always be true, since seedlings of deciduous broad-leaved and evergreen broad-leaved species partitioned regeneration niches based on light more so than topography. We propose that coexistence of deciduous broad-leaved and evergreen broadleaved species can strongly depend upon canopy disturbance to create a mosaic of habitat patches, including high light gaps favouring regeneration of deciduous broad-leaved species.
Abstract Roots are essential to the diversity and functioning of plant communities, but trade‐offs in rooting strategies are still poorly understood. We evaluated existing frameworks of rooting ...strategy trade‐offs and tested their underlying assumptions, guided by the hypothesis that community‐level rooting strategies are best described by a combination of variation in organ‐level traits, plant‐level root:shoot allocation and symbiosis‐level mycorrhizal dependency. We tested this hypothesis using data on plant community structure, above‐ and below‐ground biomass, eight root traits including mycorrhizal colonisation and soil properties from an edaphic gradient driven by elevation and water availability in sandhills prairie, Nebraska, USA. We found multidimensional trade‐offs in rooting strategies represented by a two‐way productivity‐durability trade‐off axis (captured by root length density and root dry matter content) and a three‐way resource acquisition trade‐off between specific root length, root:shoot mass ratio and mycorrhizal dependence. Variation in rooting strategies was driven to similar extents by interspecific differences and intraspecific responses to soil properties. Organ‐level traits alone were insufficient to capture community‐level trade‐offs in rooting strategies across the edaphic gradient. Instead, trait variation encompassing organ, plant and symbiosis levels revealed that consideration of whole‐plant phenotypic integration is essential to defining multidimensional trade‐offs shaping the functional variation of root systems. Read the free Plain Language Summary for this article on the Journal blog.
Summary
The Photochemical Reflectance Index (PRI) provides an optical indicator of photosynthetic light‐use efficiency, photoprotection, and stress in plants. Although PRI can be applied in remote ...sensing, its interpretation depends on irradiance, which is hard to obtain from satellite or airborne imagery.
To quantify forest photoprotective responses remotely, we developed a framework for modeling and interpreting PRI‐light responses of individual trees and species using airborne imaging spectrometry coupled with georeferenced forest inventory data from a temperate broad‐leaved forest. We derived an irradiance proxy, used hierarchical modeling to analyze PRI‐light responses, and developed a framework of physiological interpretations of model parameters as facultative and constitutive components of photoprotection.
Photochemical Reflectance Index declined with illumination, and PRI‐light relationships varied with landscape position and among tree crowns and species. More sun‐exposed foliage had lower intercepts and slopes of the relationship, indicating greater constitutive, but less facultative, photoprotection.
We show that tree photoprotective strategies can be quantified at multiple scales using airborne hyperspectral data in structurally complex forests. Our findings and approach have important implications for the remote sensing of forest stress by offering a new way to assess functional diversity through dynamic differences in photoprotection and photosynthetic downregulation and providing previsual indicators of forest stress.
While work in temperate forests suggests that there are consistent differences in plant–soil feedback (PSF) between plants with arbuscular and ectomycorrhizal associations, it is unclear whether ...these differences exist in tropical rainforests. We tested the effects of mycorrhizal type, phylogenetic relationships to overstory species, and soil fertility on the growth of tree seedlings in a tropical Bornean rainforest with a high diversity of both ectomycorrhizal and arbuscular mycorrhizal trees. We found that ectomycorrhizal tree seedlings had higher growth in soils conditioned by close relatives and that this was associated with higher mycorrhizal colonization. By contrast, arbuscular mycorrhizal tree seedlings generally grew more poorly in soils conditioned by close relatives. For ectomycorrhizal species, the phylogenetic trend was insensitive to soil fertility. For arbuscular mycorrhizal seedlings, however, the effect of growing in soils conditioned by close relatives became increasingly negative as soil fertility increased. Our results demonstrate consistent effects of mycorrhizal type on plant–soil feedbacks across forest biomes. The positive effects of ectomycorrhizal symbiosis may help explain biogeographic variation across tropical forests, such as familial dominance of the Dipterocarpaceae in southeast Asia. However, positive feedbacks also raise questions about the role of PSFs in maintaining tropical diversity.
Plants interact with a diversity of microorganisms, and there is often concordance in their community structures. Because most community‐level studies are observational, it is unclear if such ...concordance arises because of host specificity, in which microorganisms or plants limit each other's occurrence. Using a reciprocal transplant experiment, we tested the hypothesis that host specificity between trees and ectomycorrhizal fungi determines patterns of tree and fungal soil specialisation. Seedlings of 13 dipterocarp species with contrasting soil specialisations were seeded into plots crossing soil type and canopy openness. Ectomycorrhizal colonists were identified by DNA sequencing. After 2.5 years, we found no evidence of host specificity. Rather, soil environment was the primary determinant of ectomycorrhizal diversity and composition on seedlings. Despite their close symbiosis, our results show that ectomycorrhizal fungi and tree communities in this Bornean rain forest assemble independently of host‐specific interactions, raising questions about how mutualism shapes the realised niche.
The functional basis of tree growth is often evaluated based on trunk diameter even though diameter is only one dimension of growth that may not be an integrative measure of resource allocation.
We ...tested the hypothesis that growth—functional trait relationships are stronger when key sources of variation in tree growth are also accounted for, namely tree height and DBH, as well as size‐related variation in wood density and seed production using data from 3881 trees of 24 species in a subtropical forest using ordinary least square regression and standard major axis regression.
Wood density varied with tree size for 14 of 24 species, generally increasing with size. For 18 of 24 species, the correlations of leaf mass per area and an index of photosynthetic investment (PI) with biomass growth was stronger than with diameter growth rate. Juveniles did not show stronger relationships than adults but biomass growth adding up with seed production showed stronger relationships with PI than biomass growth alone for three of eight species.
Synthesis. Thus, our study helps resolve a paradox of trait‐based ecology, that is, weak growth—trait relationships, as stronger relationships emerged when accounting for more sources of intraspecific, among‐tree variation in resource allocation.
摘要
尽管胸径只是树木生长的其中一方面而非反映资源分配整合的指标，树木生长与功能性状的关系常常基于树木胸径的生长来检验。
我们利用亚热带森林24个树种3881株树木的数据通过最小二乘法和主坐标回归检验了一个假设:当生长速率的关键变异来源(包括树高、胸径、和与大小相关的木材密度与种子产量的变异)纳入考虑后，将会检验到更强的生长‐性状关系。
在14/24个树种中，木材密度随树木大小变化，总的来说，随个体大小增加而增加。在18/24的树种中，单位面积叶质量和光合投资指数 (PI) 与生物量生长率的关系比与胸径生长率强。幼年树木未显示比成年树木更强的关系，但是在3/8的树种中生物量生长和种子产量的和与PI的关系比单生物量生长更强。
综合:将更多种内的、种间资源分配的差异考虑在内的时候，更强的生长‐性状关系在我们的研究中出现了。因此我们的研究有助于解决基于功能性状的生态学中一个矛盾，即性状反映生长表现的预期及实际中检测到的弱的生长‐性状关系之间的矛盾。
Strong relationships between aboveground biomass growth rate and functional trait expression of trees were found when accounting for individual‐level variation in leaf and wood traits, tree diameter, and tree height for 23 species in a subtropical forest where a canopy crane enabled precise measurement of tree heights.
How the dramatic vertical environmental gradients in closed canopy forests shape intraspecific variation in the functional traits of tree species and their ecological strategies is not well ...understood. In an Asian subtropical forest, we tested the hypothesis that, because species’ maximum height and shade tolerance determine the lifetime environmental variation of a tree, they should be correlated with the magnitude of intraspecific variation in leaf traits and how strongly it depends on tree size.
We collected data on three vertical environmental variables, tree size and four leaf traits of 3,880 trees of 24 species in a subtropical forest. Air temperature and relative humidity displayed linear, and insolation displayed nonlinear, variation with height above‐ground. Intraspecific trait variation (ITV) varied significantly among species, for all but one understorey tree species, and also varied with tree size for at least one trait. Many trait‐size relationships were nonlinear with inflection points near the height where insolation dramatically increased. While ITV did not correlate with species’ maximum height nor shade tolerance, the amount of ITV explained by size (SDTV) and the rate of change in trait expression with size did.
Greater ITV is thought to be associated with greater environmental heterogeneity, and yet strong evidence supporting this has not always been found. Our findings shed new light on how trait plasticity is phenotypically integrated with tree species’ ecological strategy by pointing to the importance of accounting for tree size, since SDTV, rather than ITV, was associated with strategy variation in maximum height and shade tolerance.
Our study improves understanding of tree size's effect on leaf trait expression, and implies that SDTV is not only a key mechanism promoting interspecific variation in tree stature, contributing to species coexistence via vertical niche partitioning, but is also likely to influence the effects of climate change on forests by constraining tree responses to vertical environmental gradients.
A free Plain Language Summary can be found within the Supporting Information of this article.
摘要
生境因子的垂直梯度在郁闭林中如何塑造树种功能性状的种内差异及树种的生态策略并不为人所了解。在鼎湖山亚热带森林中，我们收集了垂直方向三个生境因子（光、温、气）、24个树种3880株树木的胸径、树高和4个叶功能性状（叶面积、叶厚度、比叶面积、叶干物质含量）的数据，来检验以下假说：因为物种的最大树高和耐阴性决定了树木终身经历的垂直梯度上的生境异质性，它们也应该与树种功能性状的种内变异程度（ITV）及其对个体大小的依赖程度（SDTV）有关。
结果发现：1) 气温和相对湿度与距离地面的高度呈线性，而光照呈非线性关系。2) ITV在不同物种间有明显的差异，且除了一个物种外，其余物种至少有一个叶功能性状与个体大小有关。3）很多性状‐个体大小关系是非线性的，且在光照开始猛然增加的高度附近存在拐点。4）ITV与最大树高和耐阴性几乎不存在相关性，但种内变异被个体大小解释的部分及功能性状随个体大小改变的程度与最大树高和耐阴性存在显著关系。
更大的种内变异往往被认为与更大的生境变异有关，但是这个假设并不总是被证据支持的。本研究结果表明SDTV而非ITV与树种的最大树高及耐阴性有关，指出考虑树木个体的大小是分析树木如何通过调整功能性状来适应垂直梯度上的生境变异的关键，为构建表型可塑性与物种生态策略的联系提供了新的思路。
本研究加深了个体大小与功能性状相互关系的了解，并暗示SDTV不仅是引起树种大小种间差异的关键机制，还有利于物种通过垂直梯度上生态化的分化实现共存，而且很有可能通过约束树木对垂直环境梯度来调整气候变化对森林的影响。
A free Plain Language Summary can be found within the Supporting Information of this article.
Polyploidy has played an important role in angiosperm diversification, but how polyploidy contributes to reproductive isolation remains poorly understood. Most work has focused on postzygotic ...reproductive barriers, and the influence of ploidy differences on prezygotic barriers is understudied. To address these gaps, we quantified hybrid occurrence, interspecific self-compatibility differences, and the contributions of multiple pre- and postzygotic barriers to reproductive isolation between diploid Erythronium mesochoreum (Liliaceae) and its tetraploid congener Erythronium albidum. Reproductive isolation between the study species was nearly complete, and naturally occurring hybrids were infrequent and largely sterile. Although postzygotic barriers effected substantial reproductive isolation when considered in isolation, the study species' spatial distributions and pollinator assemblages overlapped little, such that interspecific pollen transfer is likely uncommon. We did not find evidence that E. albidum and E. mesochoreum differed in mating systems, indicating that self-incompatibility release may not have fostered speciation in this system. Ultimately, we demonstrate that E. albidum and E. mesochoreum are reproductively isolated by multiple, hierarchically-operating barriers, and we add to the currently limited number of studies demonstrating that early acting barriers such as pollinator-mediated isolation can be important for effecting and sustaining reproductive isolation in diploid-polyploid systems.
• Arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (EMF) produce contrasting plant–soil feedbacks, but how these feedbacks are constrained by lithology is poorly understood.
• We ...investigated the hypothesis that lithological drivers of soil fertility filter plant resource economic strategies in ways that influence the relative fitness of trees with AMF or EMF symbioses in a Bornean rain forest containing species with both mycorrhizal strategies.
• Using forest inventory data on 1245 tree species, we found that although AMF-hosting trees had greater relative dominance on all soil types, with declining lithological soil fertility EMF-hosting trees became more dominant. Data on 13 leaf traits and wood density for a total of 150 species showed that variation was almost always associated with soil type, whereas for six leaf traits (structural properties; carbon, nitrogen, phosphorus ratios, nitrogen isotopes), variation was also associated with mycorrhizal strategy. EMF-hosting species had slower leaf economics than AMF-hosts, demonstrating the central role of mycorrhizal symbiosis in plant resource economies.
• At the global scale, climate has been shown to shape forest mycorrhizal composition, but here we show that in communities it depends on soil lithology, suggesting scale-dependent abiotic factors influence feedbacks underlying the relative fitness of different mycorrhizal strategies.
Stress memory refers to the observation that an initial, sub-lethal stress alters plants' responses to subsequent stresses. Previous transcriptome analyses of maize seedlings exposed to a repeated ...dehydration stress has revealed the existence of transcriptional stress memory in
. Whether drought-related physiological responses also display memory and how transcriptional memory translates into physiological memory are fundamental questions that are still unanswered. Using a systems-biology approach we investigate whether/how transcription memory responses established in the genome-wide analysis of
correlate with 14 physiological parameters measured during a repeated exposure of maize seedlings to dehydration stress. Co-expression network analysis revealed ten gene modules correlating strongly with particular physiological processes, and one module displaying strong, yet divergent, correlations with several processes suggesting involvement of these genes in coordinated responses across networks. Two processes key to the drought response, stomatal conductance and non-photochemical quenching, displayed contrasting memory patterns that may reflect trade-offs related to metabolic costs versus benefits of cellular protection. The main contribution of this study is the demonstration of coordinated changes in transcription memory responses at the genome level and integrated physiological responses at the cellular level upon repetitive stress exposures. The results obtained by the network-based systems analysis challenge the commonly held view that short-term physiological responses to stress are primarily mediated biochemically.
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