基于功能性状的常绿阔叶植物防火性能评价

植物功能性状不仅便于评价植物的防火性能,也有利于筛选防火植物。本研究以宁波地区的29个常绿木本植物为对象,在测定植物比叶面积、叶干物质含量、叶片含水量、枝条干物质含量和树皮厚度5个功能性状,以及鲜叶的7个防火性能指标的基础上,通过因子分析将防火性能指标划分为抗燃性f_a(包含抗火性因子f₁和燃烧速度因子f₂2个公因子)与燃烧性f_b 2个防火因子,然后利用Pearson相关和偏相关建立了5个功能性状与各个防火因子的相关性,并对29物种的防火性能进行评价。结果表明：1)比叶面积和树皮厚度与抗火性因子f₁,枝条干物质含量、树皮厚度和当年生叶片含水量与燃烧速度因子f₂,比叶面积与抗燃性因子f_a,叶片干物质含量、比叶面积和当年生叶片含水量与燃烧性因子f_b间存在显著的相关关系;2)偏相关简化植物防火性状后,比叶面积和叶干物质含量分别对抗燃性因子f_a与燃烧性因子f_b的指示性最好;3)分别基于功能性状和燃烧试验的物种抗燃性排序相似度为0.80。本研究证明,基于简易观测的植物功能性状可较好地反映树种的抗火性和燃烧性,可作为植物防火性能有效的评价方法。     

Variations in leaf morphological and chemical traits in response to life stages,plant functional types,and habitat types in an old-growth temperate forest

Intraspecific leaf trait variations are becoming a topic of interest for many ecologists because individual-based traits are essentially the drivers of variations at the community level. Six coexisting major tree species in an old-growth temperate forest, Northeast China (i.e., Abies nephrolepis, Pinus koraiensis, Acer mono, Fraxinus mandshurica, Tilia amurensis, and Ulmus laciniata) were sampled, and three habitat types (i.e., Hab I: high soil organic carbon with a moderate slope; Hab II: low soil organic carbon with a gentle slope; and Hab III: low soil organic carbon with a strong slope) were used in the plot. We performed a two-way ANOVA to compare the specific leaf area (SLA), leaf dry matter content (LDMC), leaf nitrogen content (LNC), leaf phosphorus content (LPC), and leaf carbon content (LCC) between saplings (1 < DBH ≤ 5 cm) and adults (DBH ≥ 10 cm) and between habitat types within species. We simultaneously evaluated the effects of life stage, plant functional type, and habitat type on the six leaf traits. Our results showed that life stage and habitat type had varied influences on the leaf traits of the six species. Life stage was an important determinant for all leaf traits. Plant functional type was included in the best models for SLA, LNC, and LCC. Habitat type had a greater influence on LDMC than SLA. Meanwhile, habitat type had a greater influence on LNC and LPC than LCC. The correlation between leaf traits with local environmental factors varied across different plant functional types and life stages. We suggest conducting individual-based analyses of leaf trait variations according to plant functional type and life stage to understand the plant life strategies along an environmental gradient may improve understanding of the forest dynamics in an old-growth temperate forest.     

松嫩草地66种草本植物叶片性状特征

植物叶片功能性状及其相互关系越来越受到关注.以松嫩草地66种草本植物为研究对象,测量叶片干物质含量、比叶面积、叶片厚度、叶片氮含量、叶片磷含量、叶绿素含量和类胡萝卜素含量,检验性状间的相互关系,比较不同功能群(多年生根茎禾草,多年生丛生禾草,多年生杂类草,1年生或2年生草本)间性状的差异性.结果表明,叶片厚度变异系数最大,比叶面积、叶片氮含量、叶片磷含量、叶绿素含量和类胡萝卜素含量之间存在显著的正相关关系;叶片于物质含量与叶片磷含量没有显著的相关关系,与其它叶片性状呈显著的负相关关系;叶片厚度只与叶片干物质含量和比叶面积呈显著的负相关关系,与其它叶片性状不相关.叶片干物质含量、比叶面积、叶片厚度、叶片氮、磷含量在4个功能群间差异显著,叶绿素含量和类胡萝卜素含量在各个功能群间差异不显著;多年生根茎禾草和多年生丛生禾草叶片的7个性状差异不显著;多年生根茎禾草和多年生丛生禾草的叶片干物质含量高于多年生杂类草和1年生或2年生草本,其它性状小于这两个功能群.     

Stem and leaf hydraulics of congeneric tree species from adjacent tropical savanna and forest ecosystems

Leaf and stem functional traits related to plant water relations were studied for six congeneric species pairs, each composed of one tree species typical of savanna habitats and another typical of adjacent forest habitats, to determine whether there were intrinsic differences in plant hydraulics between these two functional types. Only individuals growing in savanna habitats were studied. Most stem traits, including wood density, the xylem water potential at 50% loss of hydraulic conductivity, sapwood area specific conductivity, and leaf area specific conductivity did not differ significantly between savanna and forest species. However, maximum leaf hydraulic conductance (K _leaf) and leaf capacitance tended to be higher in savanna species. Predawn leaf water potential and leaf mass per area were also higher in savanna species in all congeneric pairs. Hydraulic vulnerability curves of stems and leaves indicated that leaves were more vulnerable to drought-induced cavitation than terminal branches regardless of genus. The midday K _leaf values estimated from leaf vulnerability curves were very low implying that daily embolism repair may occur in leaves. An electric circuit analog model predicted that, compared to forest species, savanna species took longer for their leaf water potentials to drop from predawn values to values corresponding to 50% loss of K _leaf or to the turgor loss points, suggesting that savanna species were more buffered from changes in leaf water potential. The results of this study suggest that the relative success of savanna over forest species in savanna is related in part to their ability to cope with drought, which is determined more by leaf than by stem hydraulic traits. Variation among genera accounted for a large proportion of the total variance in most traits, which indicates that, despite different selective pressures in savanna and forest habitats, phylogeny has a stronger effect than habitat in determining most hydraulic traits.     

Drought responses,phenotypic plasticity and survival of Mediterranean species in two different microclimatic sites

• Climate models predict a further drying of the Mediterranean summer. One way for plant species to persist during such climate changes is through acclimation. Here, we determine the extent to which trait plasticity in response to drought differs between species and between sites, and address the question whether there is a trade‐off between drought survival and phenotypic plasticity.
• Throughout the summer we measured physiological traits (photosynthesis – A_max, stomatal conductance – g_s, transpiration – E, leaf water potential – ψl) and structural traits (specific leaf area – SLA, leaf density – LD, leaf dry matter content – LDMC, leaf relative water content – LRWC) of leaves of eight woody species in two sites with slightly different microclimate (north‐ versus south‐facing slopes) in southern Spain. Plant recovery and survival was estimated after the summer drought period.
• We found high trait variability between species. In most variables, phenotypic plasticity was lower in the drier site. Phenotypic plasticity of SLA and LDMC correlated negatively with drought survival, which suggests a trade‐off between them. On the other hand, high phenotypic plasticity of SLA and LDMC was positively related to traits associated with rapid recovery and growth after the drought period.
• Although phenotypic plasticity is generally seen as favourable during stress conditions, here it seemed beneficial for favourable conditions. We propose that in environments with fluctuating drought periods there can be a trade‐off between drought survival and growth during favourable conditions. When climate become drier, species with high drought survival but low phenotypic plasticity might be selected for.

     

Co-ordination between leaf biomechanical resistance and hydraulic safety across 30 sub-tropical woody species

Background and AimsLeaf biomechanical resistance protects leaves from biotic and abiotic damage. Previous studies have revealed that enhancing leaf biomechanical resistance is costly for plant species and leads to an increase in leaf drought tolerance. We thus predicted that there is a functional correlation between leaf hydraulic safety and biomechanical characteristics.MethodsWe measured leaf morphological and anatomical traits, pressure–volume parameters, maximum leaf hydraulic conductance (K_leaf-max), leaf water potential at 50 % loss of hydraulic conductance (P50_leaf), leaf hydraulic safety margin (SM_leaf), and leaf force to tear (F_t) and punch (F_p) of 30 co-occurring woody species in a sub-tropical evergreen broadleaved forest. Linear regression analysis was performed to examine the relationships between biomechanical resistance and other leaf hydraulic traits.Key ResultsWe found that higher F_t and F_p values were significantly associated with a lower (more negative) P50_leaf and a larger SM_leaf, thereby confirming the correlation between leaf biomechanical resistance and hydraulic safety. However, leaf biomechanical resistance showed no correlation with K_leaf-max, although it was significantly and negatively correlated with leaf outside-xylem hydraulic conductance. In addition, we also found that there was a significant correlation between biomechanical resistance and the modulus of elasticity by excluding an outlier.ConclusionsThe findings of this study reveal leaf biomechanical–hydraulic safety correlation in sub-tropical woody species.     

胡杨叶功能性状特征及其对地下水埋深的响应

叶片性状反映了植物对环境的适应能力及其自我调控能力。以塔里木干旱荒漠区建群种胡杨（Populus euphratica）为研究对象,通过分析自然生长状况下胡杨叶功能性状对地下水埋深（GWD）的响应及功能性状间的权衡关系,揭示胡杨对极端干旱荒漠环境的生态适应策略。结果表明：胡杨7个叶功能性状种内变异程度不同（9.20%-40.02%）,叶面积（LA）变异程度最大,叶干物质含量（LDMC）与叶片含水量（LWC）变异程度较低,GWD梯度上表现出较大的分化变异特征。叶性状在不同GWD之间差异显著（P<0.05）,与GWD呈极显著相关（P<0.01）。比叶面积（SLA）、LA、LWC与叶干重（LDM）呈极显著正相关（P<0.01）,与叶厚度（LT）、叶组织密度（LTD）、LDMC呈极显著的负相关（P<0.01）;LDMC与LT、LTD,LWC与LA、SLA呈极显著正相关（P<0.01）,反映胡杨通过叶性状间的相互调节与权衡来适应干旱荒漠环境。逐步回归分析表明LA、LT对GWD变化最敏感,可间接借助这2个性状来预测干旱荒漠区地下水埋深变化。随GWD降低,胡杨SLA、LA、LDM、LWC减小,而LT、LTD、LDMC增大,其由高生长速率、资源利用能力的开拓型策略转变为以增强自身养分储存、防御能力的保守型策略,拓宽了生态幅和增强其在干旱逆境的适合度。可见,极端干旱荒漠区胡杨形成了小的LA、SLA、LDM,大的LT、LDMC、LTD等一系列有利于减少水分散失、储存养分和增强耐旱能力的干旱性状组合,这可能是其适应干旱贫瘠环境的生态策略。     

Size‐dependent and environment‐mediated shifts in leaf traits of a deciduous tree species in a subtropical forest

AimsUnderstanding the joint effects of plant development and environment on shifts of intraspecific leaf traits will advance the understandings of the causes of intraspecific trait variation. We address this question by focusing on a widespread species Clausena dunniana in a subtropical broad‐leaved forest.MethodsWe sampled 262 individuals of C. dunniana at two major topographic habitat types, the slope and hilltop, within the karst forests in Maolan Nature Reserve in southwestern China. We measured individual plant level leaf traits (i.e., specific leaf area (SLA), leaf area, leaf dry‐matter content (LDMC), and leaf thickness) that are associated with plant resource‐use strategies. We adopted a linear mixed‐effects model in which the plant size (i.e., the first principal component of plant basal diameter and plant height) and environmental factors (i.e., topographic habitat, canopy height, and rock‐bareness) were used as independent variables, to estimate their influences on the shifts of leaf traits.Key ResultsWe found that (1) plant size and the environmental factors independently drove the intraspecific leaf trait shifts of C. dunniana, of which plant size explained less variances than environmental factors. (2) With increasing plant size, C. dunniana individuals had increasingly smaller SLA but larger sized leaves. (3) The most influential environmental factor was topographic habitat; it drove the shifts of all the four traits examined. Clausena dunniana individuals on hilltops had leaf traits representing more conservative resource‐use strategies (e.g., smaller SLA, higher LDMC) than individuals on slopes. On top of that, local‐scale environmental factors further modified leaf trait shifts.ConclusionsPlant size and environment independently shaped the variations in intraspecific leaf traits of C. dunniana in the subtropical karst forest of Maolan. Compared with plant size, the environment played a more critical role in shaping intraspecific leaf trait variations, and potentially also the underlying individual‐level plant resource‐use strategies.     

Xylem cavitation vulnerability influences tree species’ habitat preferences in miombo woodlands

Although precipitation plays a central role in structuring Africa’s miombo woodlands, remarkably little is known about plant-water relations in this seasonally dry tropical forest. Therefore, in this study, we investigated xylem vulnerability to cavitation for nine principal tree species of miombo woodlands, which differ in habitat preference and leaf phenology. We measured cavitation vulnerability (Ψ₅₀), stem-area specific hydraulic conductivity (K _S), leaf specific conductivity (K _L), seasonal variation in predawn water potential (Ψ_PD) and xylem anatomical properties [mean vessel diameter, mean hydraulic diameter, mean hydraulic diameter accounting for 95 % flow, and maximum vessel length (V _L)]. Results show that tree species with a narrow habitat range (mesic specialists) were more vulnerable to cavitation than species with a wide habitat range (generalists). Ψ₅₀ for mesic specialists ranged between ?1.5 and ?2.2 MPa and that for generalists between ?2.5 and ?3.6 MPa. While mesic specialists exhibited the lowest seasonal variation in Ψ_PD, generalists displayed significant seasonal variations in Ψ_PD suggesting that the two miombo habitat groups differ in their rooting depth. We observed a strong trade-off between K _S and Ψ₅₀ suggesting that tree hydraulic architecture is one of the decisive factors setting ecological boundaries for principal miombo species. While vessel diameters correlated weakly (P > 0.05) with Ψ₅₀, V _L was positively and significantly correlated with Ψ₅₀. Ψ_PD was significantly correlated with Ψ₅₀ further reinforcing the conclusion that tree hydraulic architecture plays a significant role in species’ habitat preference in miombo woodlands.     

Are lianas more drought-tolerant than trees? A test for the role of hydraulic architecture and other stem and leaf traits

Lianas are an important component of Neotropical forests, where evidence suggests that they are increasing in abundance and biomass. Lianas are especially abundant in seasonally dry tropical forests, and as such it has been hypothesized that they are better adapted to drought, or that they are at an advantage under the higher light conditions in these forests. However, the physiological and morphological characteristics that allow lianas to capitalize more on seasonal forest conditions compared to trees are poorly understood. Here, we evaluate how saplings of 21 tree and liana species from a seasonal tropical forest in Panama differ in cavitation resistance (P ₅₀) and maximum hydraulic conductivity (K _h), and how saplings of 24 tree and liana species differ in four photosynthetic leaf traits (e.g., maximum assimilation and stomatal conductance) and six morphological leaf and stem traits (e.g., wood density, maximum vessel length, and specific leaf area). At the sapling stage, lianas had a lower cavitation resistance than trees, implying lower drought tolerance, and they tended to have a higher potential hydraulic conductivity. In contrast to studies focusing on adult trees and lianas, we found no clear differences in morphological and photosynthetic traits between the life forms. Possibly, lianas and trees are functionally different at later ontogenetic stages, with lianas having deeper root systems than trees, or experience their main growth advantage during wet periods, when they are less vulnerable to cavitation and can achieve high conductivity. This study shows, however, that the hydraulic characteristics and functional traits that we examined do not explain differences in liana and tree distributions in seasonal forests.     

Differential impact of liana colonization on the leaf functional traits of co-occurring deciduous and evergreen trees in a tropical dry scrub forest

The present study was carried out to analyze the leaf functional traits of co-occurring evergreen and deciduous tree species in a tropical dry scrub forest. This study also intended to check whether the species with contrasting leaf habits differ in their leaf trait plasticity, responding to the canopy infestation by lianas. A total of 11 leaf functional traits were studied for eight tree species with contrasting leaf habits (evergreen and deciduous) and liana-colonization status (with or without liana). In the liana-free environment (L^–), evergreen trees had significantly higher leaf tissue density (LTD) and total chlorophyll (CHL_t) than the deciduous species. Whereas the deciduous trees had higher specific leaf area (SLA) and mass-based leaf nitrogen concentration (N_mass). The leaf trait-pair relationship in the present study agreed with the well-established global trait-pair relationships (leaf thickness (LT) vs. SLA, N_mass vs. LT, SLA vs. N_mass, and LDMC vs. SLA). There was a significant difference between L⁺ and L^– individuals in leaf area (LA), petiole length (PL), SLA, LDMC, and CHL_t in the deciduous species. On the other hand, evergreen species showed marked differences across LT, SLA, LTD, N_mass, and chlorophyll components between L⁺ and L^– individuals of the same species. The results revealed the differential impact of liana colonization on the host trees with contrasting leaf habits. The deciduous species with the acquisitive strategy can have a competitive advantage over evergreen species in the exposed environments (L^–), whereas evergreen species with shade-tolerant properties were better acclimated to the shaded environments (L⁺). Therefore, liana colonization can significantly impact the C-fixation strategies of the host trees by altering their light environment and further, the magnitude of such impact may vary among species of different leaf habits. The result also indicated the patterns of convergence and divergence in some of the leaf functional traits between evergreen and deciduous species explaining the patterns of species co-existence.

     

Congruency analysis of species ranking based on leaf traits: which traits are the more reliable?

Nine leaf traits (area, fresh weight, dry weight, volume, density, thickness, specific leaf area (SLA), dry matter content (LDMC), leaf nitrogen content (LNC)) from ten plant species at eight sites in southern mediterranean France were investigated in order to assess their variability along a climatic gradient and their ranking congruency power. After examination of trait correlation patterns, we reduced the nine initial leaf traits to four traits, representative of three correlation groups: allometric traits (dry weight), functional traits (SLA and dry matter percentage) and Leaf Thickness. We analysed the variability of these four leaf traits at species and site level. We observed that between species variation (between 64.5 for SLA and 91% for LDMC) is higher than within species variation. Allowing a good congruency of species ranking assessed by spearman rank correlation () and a good reallocation of individuals to species by discriminant analysis. A site level variability (between 0.7% for Dry weight and 6.9% for SLA) was identified and environmental parameters (altitude, temperature, precipitation, nitrogen, pH) were considered as probable control factors. We found significant correlation between SLA, LDMC and the average minimum temperature (respectively r=0.87 and r=-0,9) and no correlation for the other traits or environmental parameters. Furthermore, we conclude that two leaf traits appear to be central in describing species: specific leaf area (SLA), percentage of dry matter (LDMC. While, SLA and LDMC are strongly correlated, LDMC appears to be less variable than SLA. According to our results the Dry Matter Content (or its reversal Leaf Water Content) appears the best leaf trait to be quantified for plant functional screening. Leaf thickness appeared to be rather uncorrelated with other leaf traits and show no environmental contingency; its variability could not have been explained in this study. Further studies should focus on this trait. This revised version was published online in June 2006 with corrections to the Cover Date.     

Do Clonal and Bud Bank Traits Vary in Correspondence with Soil Properties and Resource Acquisition Strategies? Patterns in Alpine Communities in the Scandian Mountains

Plant traits associated with resource acquisition strategies (specific leaf area (SLA), leaf dry matter content (LDMC), leaf size and plant height) change along gradients of soil properties, being the most conservative in a resource-poor environment and the most dynamic in a resource-rich environment. Clonal attributes also vary along soil and other environmental conditions. We hypothesized that in alpine communities in the Scandian Mts. (1) the average composition of traits in a plant assemblage in terms of i) the predominance of different clonal growth organ types, ii) the number of buds in the bud bank, iii) the distribution of the bud-bank (above- and below ground), iv) the distance of lateral spread and v) the longevity of plant – offspring connections would change along a gradient of soil properties and (2) that this variation would be in correspondence with that of traits associated with resource acquisition strategies (SLA, LDMC, leaf size and plant height). Analysis of clonal and bud bank traits for species of alpine communities supported our first hypothesis: with decreasing soil quality the most common clonal growth organs were rhizomes, and there was a predominance of perennial bud banks located at the soil surface or below-ground, low rates of lateral spread and long persistence of plant – offspring connections. Our second hypothesis was partly supported. As predicted, at the level of the plant assemblage, these clonal and bud bank traits were positively associated with LDMC, and negatively with leaf size and plant height. These observations reinforce the hypotheses about trade-offs between acquisition and retention strategies in plants. The only result that was in contradiction with our expectations was the lack of correspondence between clonal and bud bank traits and SLA that could be attributed to errors associated to the measurement of the area of narrow and small leaves or to the dependence of the SLA index on species-specific morphological attributes.     

去除干扰对内蒙古典型草原植物叶片功能属性的影响

以内蒙古典型草原为研究对象,选取放牧和割草、去除放牧、去除放牧和割草样地进行群落调查和叶片属性测量,比较分析各样地土壤性质、群落生产力及主要物种的比叶面积(SLA,Specific Leaf Area)、叶片干物质含量(LDMC,Leaf Dry Matter Content)、叶片氮含量(LNC,Leaf Nitrogen Concentration)在个体、功能群和群落水平对去除干扰的响应。结果表明,1)去除干扰处理在短期对土壤特性和群落生产力的影响不显著;2)多数物种在放牧和割草样地SLA较低,说明典型草原多数物种的SLA表现为放牧逃避;3)不同功能群植物叶片属性对去除干扰的响应不一致,去除放牧后,多年生杂类草的SLA和LDMC不受影响,但LNC变小;多年生禾草的SLA增加,而LDMC和LNC无显著变化。一年生植物在去除放牧和割草后,LNC显著增加。去除割草后,多年生禾草SLA减小,而多年生杂类草SLA、LNC增加,LDMC减小;4)在群落水平,放牧和割草样地由于较占优势的多年生禾草SLA较低,群落比叶面积最低,在去除放牧和割草样地,群落叶片氮含量显著增加;5)在内蒙古典型草原,LDMC能够很好地将多年生禾草和多年生杂类草区分,SLA在个体、功能群和群落水平均比LDMC敏感。     

黄土高原子午岭不同森林群落叶功能性状

对黄土高原子午岭地区5种主要森林群落中重要值>0.1的物种叶功能性状进行了比较,结果表明:1)叶干物质含量(LDMC)与比叶面积(SLA)呈负相关;SLA与叶厚度(LT)呈负相关,但与叶氮含量(LNC)和叶磷含量(LPC)呈正相关;LT与LNC、LPC和叶钾含量(LKC)呈负相关;LNC、LPC和LKC三者之间均呈正相关。2)坡位是影响叶大小(LS)、LT、LNC和LKC的主要地形因子,海拔对LPC和SLA的影响最大,而坡向则是影响LDMC的主要因子。因此,叶功能性状之间所呈现的特征及其对立地条件的适应都表现出了植物的生态策略。3)各群落间的乔木层叶功能性状均有显著差异,灌木层的叶功能性状无显著差异,而草本层除了LDMC无显著差异(P>0.05)外,其他叶功能性状均有显著差异,说明群落的叶功能性状的大小取决于群落内物种的叶功能性状及其重要值。     

柯-青冈常绿阔叶林优势树种叶片性状变异及适应策略

厘清叶片功能性状的变异及性状间的权衡关系，对揭示植物对环境变化的响应及适应策略具有重要意义。以中亚热带柯(Lithocarpus glaber)-青冈(Cyclobalanopsis glauca)常绿阔叶林为对象，测量了1 hm²固定监测样地内6个优势树种的叶面积(LA)、比叶面积(SLA)、干物质含量(LDMC)、叶片厚度(LT)、叶片碳(LC)、叶片氮(LN)、叶片磷(LP)含量和叶片碳氮比(LC ∶ LN)8个功能性状，采用多重比较、主成分分析(PCA)法分析了群落叶片功能性状的生活型、种内和种间变异及性状间关系。结果表明：(1)群落内叶片功能性状种内、种间差异显著，变异中等(CV： 0.02-0.59)，其结构性状的可塑性较化学性状保守，变异格局符合"性状空间变异分割假说"；针叶树种的LA、SLA显著低于阔叶树种，常绿树种的LC和LDMC最小，而落叶树种的SLA、LN和LP最大以及LT和LC ∶ LN最小。(2)群落叶片功能性状变异主要来源于生活型和种间变异，种内变异亦有显著贡献；生活型对多数性状的贡献率较大，其对LDMC、LC ∶ LN的贡献分别高达93.11%和91.76%；种间变异(LDMC除外)对结构性状的贡献率均高于化学性状；种内变异对LP的贡献率(23.66%)较种间变异高。(3)叶片性状之间多表现出显著相关关系，针叶树和阔叶树在PCA排序图中聚集于不同区域，叶经济型谱在柯-青冈群落中具有适用性。不同树种通过叶片结构、化学性状之间的权衡策略来适应环境变化，从而实现群落物种共存。结果可为理解森林群落物种的环境适应策略、预测群落动态变化和制定植被恢复措施提供科学依据。     

Hydraulic characteristics and leaf water use efficiency in trees from tropical montane habitats

This study was carried out in pioneer and successional forest tree species in a lower montane tropical forest with seasonal rains. We tested whether pioneer species feature high hydraulic conductance allowing them to use water profusely at leaf level. Conversely, forest species may have relatively low hydraulic conductance accompanied with better control over water use. This may lead in turn to pioneer species being at a relatively higher risk of shoot water potential falling below the threshold value at which cavitations occur compared to forest. Specific hydraulic conductance ( K _s) measured during the wet season was comparable between pioneers and forest species. During drought, K _s was significantly reduced, and species of both plant groups responded to this by modifying the relationship between conducting area and leaf area (Huver value), such that leaf specific conductivity ( K _l) was unaffected. Thus, leaf area seemed to be adjusted to maintain constant hydraulic sufficiency during drought. Pioneer species were more efficient in conducting water to their leaves but had low control over water use compared to forest species. A trade-off between water transport and leaf water use efficiency was suggested. These ecophysiological differences may have an impact on the performance of the species occupying contrasting habitats. Nonetheless, drought-induced embolisms occurred in trees growing in both open and forest habitats. Overall, during drought, adjustment of leaf area occurred in order to maintain a homeostasis of some physiological traits (leaf-specific conductivity and carbon assimilation).     

Shade tolerance and herbivory are associated with RGR of tree species via different functional traits

• Relative growth rate (RGR) plays an important role in plant adaptation to the light environment through the growth potential/survival trade‐off. RGR is a complex trait with physiological and biomass allocation components. It has been argued that herbivory may influence the evolution of plant strategies to cope with the light environment, but little is known about the relation between susceptibility to herbivores and growth‐related functional traits.
• Here, we examined in 11 evergreen tree species from a temperate rainforest the association between growth‐related functional traits and (i) species’ shade‐tolerance, and (ii) herbivory rate in the field. We aimed at elucidating the differential linkage of shade and herbivory with RGR via growth‐related functional traits.
• We found that RGR was associated negatively with shade‐tolerance and positively with herbivory rate. However, herbivory rate and shade‐tolerance were not significantly related. RGR was determined mainly by photosynthetic rate (A_max) and specific leaf area (SLA). Results suggest that shade tolerance and herbivore resistance do not covary with the same functional traits. Whereas shade‐tolerance was strongly related to A_max and to a lesser extent to leaf mass ratio (LMR) and dark respiration (R_d), herbivory rate was closely related to allocation traits (SLA and LMR) and slightly associated with protein content.
• The effects of low light on RGR would be mediated by A_max, while the effects of herbivory on RGR would be mediated by SLA. Our findings suggest that shade and herbivores may differentially contribute to shape RGR of tree species through their effects on different resource‐uptake functional traits.

     

Contrasting effects of plant inter‐ and intraspecific variation on community trait responses to restoration of a sandy grassland ecosystem

Changes in plant community traits along an environmental gradient are caused by interspecific and intraspecific trait variation. However, little is known about the role of interspecific and intraspecific trait variation in plant community responses to the restoration of a sandy grassland ecosystem. We measured five functional traits of 34 species along a restoration gradient of sandy grassland (mobile dune, semi‐fixed dune, fixed dune, and grassland) in Horqin Sand Land, northern China. We examined how community‐level traits varied with habitat changes and soil gradients using both abundance‐weighted and non‐weighted averages of trait values. We quantified the relative contribution of inter‐ and intraspecific trait variation in specific leaf area (SLA), leaf dry matter content (LDMC), leaf carbon content (LCC), leaf nitrogen content (LNC), and plant height to the community response to habitat changes in the restoration of sandy grassland. We found that five weighted community‐average traits varied significantly with habitat changes. Along the soil gradient in the restoration of sandy grassland, plant height, SLA, LDMC, and LCC increased, while LNC decreased. For all traits, there was a greater contribution of interspecific variation to community response in regard to habitat changes relative to that of intraspecific variation. The relative contribution of the interspecific variation effect of an abundance‐weighted trait was greater than that of a non‐weighted trait with regard to all traits except LDMC. A community‐level trait response to habitat changes was due largely to species turnover. Though the intraspecific shift plays a small role in community trait response to habitat changes, it has an effect on plant coexistence and the maintenance of herbaceous plants in sandy grassland habitats. The context dependency of positive and negative covariation between inter‐ and intraspecific variation further suggests that both effects of inter‐ and intraspecific variation on a community trait should be considered when understanding a plant community response to environmental changes in sandy grassland ecosystems.     

Plant Trait Assembly Affects Superiority of Grazer's Foraging Strategies in Species-Rich Grasslands

Background

Current plant – herbivore interaction models and experiments with mammalian herbivores grazing plant monocultures show the superiority of a maximizing forage quality strategy (MFQ) over a maximizing intake strategy (MI). However, there is a lack of evidence whether grazers comply with the model predictions under field conditions.

Methodology/Findings

We assessed diet selection of sheep (Ovis aries) using plant functional traits in productive mesic vs. low-productivity dry species-rich grasslands dominated by resource-exploitative vs. resource-conservative species respectively. Each grassland type was studied in two replicates for two years. We investigated the first grazing cycle in a set of 288 plots with a diameter of 30 cm, i.e. the size of sheep feeding station. In mesic grasslands, high plot defoliation was associated with community weighted means of leaf traits referring to high forage quality, i.e. low leaf dry matter content (LDMC) and high specific leaf area (SLA), with a high proportion of legumes and the most with high community weighted mean of forage indicator value. In contrast in dry grasslands, high community weighted mean of canopy height, an estimate of forage quantity, was the best predictor of plot defoliation. Similar differences in selection on forage quality vs. quantity were detected within plots. Sheep selected plants with higher forage indicator values than the plot specific community weighted mean of forage indicator value in mesic grasslands whereas taller plants were selected in dry grasslands. However, at this scale sheep avoided legumes and plants with higher SLA, preferred plants with higher LDMC while grazing plants with higher forage indicator values in mesic grasslands.

Conclusions

Our findings indicate that MFQ appears superior over MI only in habitats with a predominance of resource-exploitative species. Furthermore, plant functional traits (LDMC, SLA, nitrogen fixer) seem to be helpful correlates of forage quality only at the community level.