Modest enhancement of nitrogen conservation via retranslocation in response to gradients in N supply and leaf N status

Plant nutrient resorption, a ubiquitous mechanism of nutrient conservation, has often been proposed to be more pronounced in infertile than fertile habitats, and in species common to infertile compared to fertile habitats, because of the presumed advantage when nutrients are scarce. However, previous studies provide weak and inconsistent empirical support for these hypotheses, although few have examined intraspecific variation across well-quantified resource gradients. This study addresses intraspecific patterns of nutrient resorption for eight species across two N availability gradients on similar soils in an N-limited oak savanna ecosystem: a long-term fire frequency gradient with a negatively correlated N fertility gradient and a long-term N fertilization gradient. We hypothesized that both resorption proficiency (the minimum nutrient level retained in a senesced leaf) and efficiency (the proportional change in leaf nutrient concentration) would decrease with increasing soil N availability and plant N status. For the seven non-N fixers, either resorption proficiency or efficiency decreased modestly in treatments with higher N availability. In contrast, the legume Amorpha canescens Pursh had higher N levels in green and senesced leaves, and resorbed N much more weakly than the non-fixers, and did not respond in terms of proficiency or efficiency to soil N availability. Across all species and sites in each N fertility gradient, a scaling analysis showed greater resorption efficiency in plants with lower N concentrations. Our data suggest that species can have modest resorption responses reflective of soil nutrient availability and differences in resorption related to their N economy that represent mechanisms of nutrient conservation in nutrient-limited soils.     

N limitation increases along a temperate forest succession: evidences from leaf stoichiometry and nutrient resorption

温带森林演替加剧了氮限制：来自叶片化学计量和养分重吸收的证据 森林生产力和碳汇功能在很大程度上取决于土壤氮和磷的有效性。然而,迄今为止,养分限制随森林演替的时间变化仍存在争议。叶片化学计量和养分重吸收是预测植物生长养分限制的重要指标。基于此,本研究测定了温带森林4个演替阶段所有木本植物叶片和凋落叶中氮和磷的含量,并分析了演替过程中非生物因子和生物因子如何影响叶片化学计量和养分重吸收。研究结果表明,在个体尺度上,叶片氮磷含量在演替末期显著增加,而叶片氮磷比无显著变化;氮的重吸收效率随演替显著增加,然而磷的重吸收效率先增加后减少;氮重吸收效率与磷重吸收效率的比值仅在演替末期显著增加。此外,植物氮素循环对土壤养分的响应比磷素循环更弱。在群落尺度上,叶片氮磷含量随森林演替呈现先降低后升高的趋势,主要受香农-维纳多样性指数和物种丰富度的影响;叶片氮磷比随演替而显著变化,主要由胸径的群落加权平均值决定;氮的重吸收效率增加,主要受物种丰富度和胸径的影响,而磷的重吸收效率相对稳定。因此,氮重吸收效率与磷重吸收效率的比值显著增加,表明随着温带森林演替,氮限制加剧。这些结果可能反映了较高生物多样性群落中物种间对有限资源的激烈竞争,强调了生物因子在驱动森林生态系统养分循环中的重要性,为中国温带和北方森林可持续经营的施肥管理提供了参考。     

氮素添加对黄土高原典型草原长芒草氮磷重吸收率及C:N:P化学计量特征的影响

 为了解氮素沉降对草地群落的影响, 通过人工氮肥添加模拟试验, 研究了黄土高原天然草地优势植物长芒草(Stipa bungeana)在不同施氮水平下叶片和立枯物碳(C)、氮(N)、磷(P)元素含量的变化特征, 探讨了N素增加对N、P重吸收率和C : N : P化学计量比的影响及其内在联系。结果表明: 氮素添加显著增加了长芒草叶片的C、N和立枯物的N、P含量, 对叶片P和立枯物C含量无显著影响; 氮素添加显著降低了长芒草的N、P重吸收率, 对照处理的N、P重吸收率最高, 分别为60.35%和
71.75%, 并且, 在相同氮素处理条件下P的重吸收率显著大于N重吸收率; 随着氮素添加量的增大, 叶片的C : N降低, N : P和C : P增加, N : P为18.25–29.01。研究表明, 黄土高原天然草地群落主要受P限制, 随氮素沉降增加, P限制进一步加剧; 长芒草较高的N、P重吸收率是保证其在贫瘠的土壤中生存的重要机制。     

Nutrient resorption and stoichiometric responses of poplar (Populus deltoids) plantations to N addition in a coastal region of eastern China

中国东部沿海杨树人工林养分重吸收和化学计量对氮添加的响应 叶片养分重吸收对土壤养分的变化很敏感。然而,我们尚不清楚氮沉降如何影响植物大量元素重吸收率。杨树(Populus deltoids)是世界上栽培最广泛的阔叶树种之一。本文研究了在氮添加条件下,杨树重吸收率及其化学计量比的规律和主要驱动因素。通过一个4年的氮添加实验,我们探究中国东部沿海两个林分(8和12年)杨树人工林重吸收率及其化学计量比对氮添加的响应。我们测定了在一系列氮添加浓度水平(0、50、100、150、300 kg N ha⁻¹ yr⁻¹)下,土壤和叶片(包括绿叶和落叶)中氮、磷、钾、钙、镁的浓度。研究结果表明,除钙元素重吸收率和钙、镁元素重吸收率化学计量比外,氮添加对两个林分大量元素重吸收率及其化学计量比都没有显著影响。氮、磷重吸收率尺度斜率在不同氮添加水平下均小于1,表明氮添加条件下,氮、磷元素重吸收率解耦。养分重吸收率与绿叶中养分含量显著正相关,表明重吸收主要受到绿叶养分调控。我们的研究结果为中国东部沿海地区12年生杨树人工林的生长受氮限制提供了直接证据。     

Global-scale patterns of nutrient resorption associated with latitude, temperature and precipitation

Aim   Nutrient resorption from senescing leaves is an important mechanism of nutrient conservation in plants, but the patterns of nutrient resorption at the global scale are unknown. Because soil nutrients vary along climatic gradients, we hypothesize that nutrient resorption changes with latitude, temperature and precipitation.
Location   Global.
Methods   We conducted a meta-analysis on a global data set collected from published literature on nitrogen (N) and phosphorus (P) resorption of woody plants.
Results    For all data pooled, both N resorption efficiency (NRE) and P resorption efficiency (PRE) were significantly related to latitude, mean annual temperature (MAT) and mean annual precipitation (MAP): NRE increased with latitude but decreased with MAT and MAP. In contrast, PRE decreased with latitude but increased with MAT and MAP. When functional groups (shrub versus tree, coniferous versus broadleaf and evergreen versus deciduous) were examined individually, the patterns of NRE and PRE in relation to latitude, MAT and MAP were generally similar.
Main conclusions   The relationships between N and P resorption and latitude, MAT and MAP indicate the existence of geographical patterns of plant nutrient conservation strategies in relation to temperature and precipitation at the global scale, particularly for PRE, which can be an indicator for P limitation in the tropics and selective pressure shaping the evolution of plant traits. Our results suggest that, although the magnitude of plant nutrient resorption might be regulated by local factors such as substrate, spatial patterns are also controlled by temperature or precipitation.     

Nutrient resorption in tropical savanna forests and woodlands of central Brazil

Nutrient limitation in Brazilian savanna (known as cerrado) presumably causes trees to maximize nutrient resorption from senesced leaves to reduce their dependence on nutrient availability. To assess patterns between nutrient resorption and soil fertility, we measured community-level nitrogen (N), phosphorus (P), and potassium (K) concentrations in mature and senesced leaves and soil fertility in the upper 50 cm soil layer in structurally diverse cerrado ecosystems in the Cuiaba Basin (CB) and Pantanal (PAN) of Mato Grosso, Brazil. Foliar nutrient concentration data were used to estimate resorption efficiency and proficiency, and correlation was used to determine whether resorption efficiency and proficiency varied across soil fertility gradients. We found that N and P resorption proficiency (NRP and PRP, respectively) and P resorption efficiency (PRE) increased significantly as total soil N (NRP) and extractable P (PRP and PRE) declined. In contrast, K resorption efficiency (KRE) declined as soil sand content and bulk density increased, which was likely due to a reduction in soil water-holding capacity. Leaf N/P ratios indicate potential N limitation and/or N + P co-limitation for ecosystems in the PAN and P limitation and/or N + P co-limitation for ecosystems in the CB, while trends in leaf N/K ratios indicate possible K or K + P co-limitation for the CB only. Our results illustrate that cerrado forests and woodlands have highly variable nutrient resorption capacities that vary predictably across soil fertility or textural gradients and indicate that cerrado communities have flexible nutrient resorption that can reduce their dependence on soil nutrient availability.     

Relationship between the Relative Limitation and Resorption Efficiency of Nitrogen vs Phosphorus in Woody Plants

Most previous studies have ascribed variations in the resorption of a certain plant nutrient to its corresponding environmental availability or level in tissues, regardless of the other nutrients’ status. However, given that plant growth relies on both sufficient and balanced nutrient supply, the nutrient resorption process should not only be related to the absolute nutrient status, but also be regulated by the relative limitation of the nutrient. Here, based on a global woody-plants dataset from literature, we test the hypothesis that plants resorb proportionately more nitrogen (or phosphorus) when they are nitrogen (or phosphorus) limited, or similar proportions of nitrogen (N) and phosphorus (P) when co-limited by both nutrients (the relative resorption hypothesis). Using the N:P ratio in green foliage as an indicator of nutrient limitation, we found an inverse relationship between the difference in the proportionate resorption of N vs P and this foliar N:P ratio, consistent across species, growth-forms, and vegetation-types globally. Moreover, according to the relative resorption hypothesis, communities with higher/lower foliar N:P (more likely P/N limited) tend to produce litter with disproportionately higher/lower N:P, causing a worsening status of P/N availability; this positive feedback may somehow be counteracted by several negative-feedback mechanisms. Compared to N, P generally shows higher variability in resorption efficiency (proportion resorbed), and higher resorption sensitivity to nutrient availability, implying that the resorption of P seems more important for plant nutrient conservation and N:P stoichiometry. Our findings elucidate the nutrient limitation effects on resorption efficiency in woody plants at the global scale, and thus can improve the understanding of nutrient resorption process in plants. This study also suggests the importance of the foliar N:P ratio as a key parameter for biogeochemical modeling, and the relative resorption hypothesis used to deduce the critical (optimal) N:P ratio for a specific plant community.     

Convergent responses of nitrogen and phosphorus resorption to nitrogen inputs in a semiarid grassland

Human activities have significantly altered nitrogen (N) availability in most terrestrial ecosystems, with consequences for community composition and ecosystem functioning. Although studies of how changes in N availability affect biodiversity and community composition are relatively common, much less remains known about the effects of N inputs on the coupled biogeochemical cycling of N and phosphorus (P), and still fewer data exist regarding how increased N inputs affect the internal cycling of these two elements in plants. Nutrient resorption is an important driver of plant nutrient economies and of the quality of litter plants produce. Accordingly, resorption patterns have marked ecological implications for plant population and community fitness, as well as for ecosystem nutrient cycling. In a semiarid grassland in northern China, we studied the effects of a wide range of N inputs on foliar nutrient resorption of two dominant grasses, Leymus chinensis and Stipa grandis. After 4 years of treatments, N and P availability in soil and N and P concentrations in green and senesced grass leaves increased with increasing rates of N addition. Foliar N and P resorption significantly decreased along the N addition gradient, implying a resorption‐mediated, positive plant–soil feedback induced by N inputs. Furthermore, N : P resorption ratios were negatively correlated with the rates of N addition, indicating the sensitivity of plant N and P stoichiometry to N inputs. Taken together, the results demonstrate that N additions accelerate ecosystem uptake and turnover of both N and P in the temperate steppe and that N and P cycles are coupled in dynamic ways. The convergence of N and P resorption in response to N inputs emphasizes the importance of nutrient resorption as a pathway by which plants and ecosystems adjust in the face of increasing N availability.     

Foliar nutrient resorption patterns of four functional plants along a precipitation gradient on the Tibetan Changtang Plateau

Nutrient resorption from senesced leaves as a nutrient conservation strategy is important for plants to adapt to nutrient deficiency, particularly in alpine and arid environment. However, the leaf nutrient resorption patterns of different functional plants across environmental gradient remain unclear. In this study, we conducted a transect survey of 12 communities to address foliar nitrogen (N) and phosphorus (P) resorption strategies of four functional groups along an eastward increasing precipitation gradient in northern Tibetan Changtang Plateau. Soil nutrient availability, leaf nutrient concentration, and N:P ratio in green leaves ([N:P]_g) were linearly correlated with precipitation. Nitrogen resorption efficiency decreased, whereas phosphorus resorption efficiency except for sedge increased with increasing precipitation, indicating a greater nutrient conservation in nutrient‐poor environment. The surveyed alpine plants except for legume had obviously higher N and P resorption efficiencies than the world mean levels. Legumes had higher N concentrations in green and senesced leaves, but lowest resorption efficiency than nonlegumes. Sedge species had much lower P concentration in senesced leaves but highest P resorption efficiency, suggesting highly competitive P conservation. Leaf nutrient resorption efficiencies of N and P were largely controlled by soil and plant nutrient, and indirectly regulated by precipitation. Nutrient resorption efficiencies were more determined by soil nutrient availability, while resorption proficiencies were more controlled by leaf nutrient and N:P of green leaves. Overall, our results suggest strong internal nutrient cycling through foliar nutrient resorption in the alpine nutrient‐poor ecosystems on the Plateau. The patterns of soil nutrient availability and resorption also imply a transit from more N limitation in the west to a more P limitation in the east Changtang. Our findings offer insights into understanding nutrient conservation strategy in the precipitation and its derived soil nutrient availability gradient.     

Combined effects of nitrogen addition and litter manipulation on nutrient resorption of Leymus chinensis in a semi‐arid grassland of northern China

Plant growth in semi‐arid ecosystems is usually severely limited by soil nutrient availability. Alleviation of these resource stresses by fertiliser application and aboveground litter input may affect plant internal nutrient cycling in such regions. We conducted a 4‐year field experiment to investigate the effects of nitrogen (N) addition (10 g N·m^?2·year^?1) and plant litter manipulation on nutrient resorption of Leymus chinensis, the dominant native grass in a semi‐arid grassland in northern China. Although N addition had no clear effects on N and phosphorus (P) resorption efficiencies in leaves and culms, N fertilisation generally decreased leaf N resorption proficiency by 54%, culm N resorption proficiency by 65%. Moreover, N fertilisation increased leaf P resorption proficiency by 13%, culm P resorption proficiency by 20%. Under ambient or enriched N conditions, litter addition reduced N and P resorption proficiencies in both leaves and culms. The response of P resorption proficiency to litter manipulation was more sensitive than N resorption proficiency: P resorption proficiency in leaves and culms decreased strongly with increasing litter amount under both ambient and enriched N conditions. In contrast, N resorption proficiency was not significantly affected by litter addition, except for leaf N resorption proficiency under ambient N conditions. Furthermore, although litter addition caused a general decrease of leaf and culm nutrient resorption efficiencies under both ambient and enriched N conditions, litter addition effects on nutrient resorption efficiency were much weaker than the effects of litter addition on nutrient resorption proficiency. Taken together, our results show that leaf and non‐leaf organs of L. chinensis respond consistently to altered soil N availability. Our study confirms the strong effects of N addition on plant nutrient resorption processes and the potential role of aboveground litter, the most important natural fertiliser in terrestrial ecosystems, in influencing plant internal nutrient cycling.     

Nutrient resorption response to fire and nitrogen addition in a semi-arid grassland

Fire and nitrogen (N) addition, both widely used grassland restoration strategies, strongly influence community composition and ecosystem functioning. However, little is known about their effects on plant nutrient resorption from senescing leaves, especially in semi-arid ecosystems. We evaluated the effects of fire, N addition (5.25 g N m⁻² yr⁻¹) and their potential interactions on nutrient resorption in five plant species in a semi-arid grassland in northern China. Foliar nutrient concentrations and resorption proficiencies and efficiencies varied substantially among species and functional groups. Fire increased green leaf N concentration ([N]g) and decreased N resorption proficiency (N RP), P resorption proficiency (P RP) and P resorption efficiency (P RE). N addition led to higher [N]g and lower N resorption, whereas it did not affect P related responses. There was no interaction between fire and N addition to affect all response variables except for green leaf P concentration ([P]g). These results suggest that fire and N addition can influence ecosystem nutrient cycling directly by changing resorption patterns and litter quality. Given the substantial interspecific variations in nutrient content and resorption and the potentially changing community composition, both fire and N addition may have indirect impacts on ecosystem nutrient cycling in this semi-arid grassland.     

去叶时间对半干旱草原植物养分回收和干草生产的影响

去叶时间对半干旱草原植物养分回收和干草生产的影响 养分回收是植物养分保存的重要策略,其对环境和管理变化的响应关系到生态系统的养分循环和生产。去叶(刈割)是影响草地植物养分回收和生产的重要途径,而去叶时间的影响尚不清楚。本研究以内蒙古典型草原生态系统为对象,设置早期去叶(生物量高峰期之前)、峰期去叶(生物量高峰期)、晚期去叶(养分回收开始后)和不去叶(对照)四个处理,探讨了去叶时间对植物养分回收和生产的影响。通过测定植物物种和群落水平氮(N)和磷(P)回收特征,量化了植物N、P回收通量以及凋落物归还通量和干草输出通量,并评估了不同去叶时间处理下割草草地系统干草产量和质量。研究结果显示,峰期和晚期去叶降低植物群落N、P回收度,而早期去叶则对二者无影响;不同去叶时间处理下植物N、P回收效率相对稳定,仅晚期去叶降低N回收效率。峰期和晚期去叶降低植物群落N、P回收通量和凋落物N、P归还通量,而早期去叶并不影响这些参数。去叶时间降低植物群落养分回收通量,但未改变植物根系养分储存,说明根系养分吸收增加可补偿养分回收通量的降低。草地干草产量和质量在峰期去叶处理下最高,晚期去叶处理下最低。本研究结果为割草草地生态系统养分循环提供了新见解,通过调整刈割时间可以平衡草原的保护与生产,在植物生物量高峰期之前割草可实现保护和可持续生产的双重目标。     

Resorption proficiency and efficiency of leaf nutrients in woody plants in eastern China

Aims (i) To explore variations in nutrient resorption of woody plants and their relationship with nutrient limitation and (ii) to identify the factors that control these variations in forests of eastern China.Methods We measured nitrogen (N) and phosphorus (P) concentrations in both green and senesced leaves of 172 woody species at 10 forest sites across eastern China. We compared the nutrient resorption proficiency (NuRP) and efficiency (NuRE) of N and P in plant leaves for different functional groups; we further investigated the latitudinal and altitudinal variations in NuRP and NuRE and the impacts of climate, soil and plant types on leaf nutrient resorptions.Important findings On average, the leaf N resorption proficiency (NRP) and P resorption proficiency (PRP) of woody plants in eastern China were 11.1mg g ? 1 and 0.65 mg g ? 1, respectively; and the corresponding N resorption efficiency (NRE) and P resorption efficiency (PRE) were 49.1% and 51.0%, respectively. Angiosperms have higher NRP (are less proficient) values and lower NRE and PRE values than gymnosperms, but there are no significant differences in NRP, PRP and PRE values between species with different leaf habits (evergreen vs. deciduous angiosperms). Trees have higher NRE and PRE than shrubs. Significant geographical patterns of plant nutrient resorption exist in forests of eastern China. In general, NRP and PRE decrease and PRP and NRE increase with increasing latitude/altitude for all woody species and for the different plant groups. Plant functional groups show more controls than environmental factors (climate and soil) on the N resorption traits (NRP and NRE), while site-related variables present more controls than plant types on PRP and PRE. NRP increases and PRP and NRE decrease significantly with increasing temperature and precipitation for the overall plants and for most groups, except that significant PRE–climate relationship holds for only evergreen angiosperms. Leaf nutrient resorption did not show consistent responses in relation to soil total N and P stoichiometry, probably because the resorption process is regulated by the relative costs of drawing nutrients from soil versus from senescing leaves. These results support our hypothesis that plants growing in P-limited habitats (low latitudes/altitudes or areas with high precipitation/temperature) should have lower PRP and higher PRE, compared with their counterparts in relatively N-limited places (high latitudes/altitudes or areas with low precipitation/temperature). Our findings can improve the understanding of variations in N and P resorption and their responses to global change, and thus facilitate to incorporate these nutrient resorption processes into future biogeochemical models.     

Low leaf N and P resorption contributes to nutrient limitation in two desert shrubs

Both water and nutrients are limiting in arid environments, and desert plants have adapted to these limitations through numerous developmental and physiological mechanisms. In the Mono Basin, California, USA, co-dominant Sarcobatus vermiculatus and Chrysothamnus nauseosus ssp. consimilis are differentially N and P limited. We hypothesized that low leaf N resorption contributes to N-limitation in Sarcobatus and that low leaf P resorption contributes to P-limitation in Chrysothamnus. As predicted, Sarcobatus resorbed proportionally 1.7-fold less N than Chrysothamnus, but reduced leaf P in senescent leaves to lower levels than Chrysothamnus (8.0–10.8-fold lower based on leaf area or mass, respectively), consistent with N, but not P limitations in Sarcobatus. Again, as predicted, Chrysothamnus resorbed proportionally 2.0-fold less P than Sarcobatus yet reduced leaf N in senescent leaves to lower levels than Sarcobatus (1.8–1.3-fold lower based on leaf area or mass, respectively), consistent with P, but not N limitations in Chrysothamnus. Leaf N and P pools were approximately 50% of aboveground pools in both species during the growing season, suggesting leaf resorption can contribute significantly to whole plant nutrient retention. This was consistent with changes in leaf N vs. P concentration as plants grew from seedlings to adults. Our results support the conclusion that N-limitation in Sarcobatus and P-limitation in Chrysothamnus are in part caused by physiological (or other) constraints that prevent more efficient resorption of N or P, respectively. For these species, differential nutrient resorption may be a key physiological component contributing to their coexistence in this saline, low resource habitat.     

Nutrient resorption patterns of plant functional groups in a tropical savanna: variation and functional significance

Green and senesced leaf nitrogen (N) and phosphorus (P) concentrations of different plant functional groups in savanna communities of Kruger National Park, South Africa were analyzed to determine if nutrient resorption was regulated by plant nutritional status and foliar N:P ratios. The N and P concentrations in green leaves and the N concentrations in senesced leaves differed significantly between the dominant plant functional groups in these savannas: fine-leaved trees, broad-leaved trees and grasses. However, all three functional groups reduced P to comparable and very low levels in senesced leaves, suggesting that P was tightly conserved in this tropical semi-arid savanna ecosystem. Across all functional groups, there was evidence for nutritional control of resorption in this system, with both N and P resorption efficiencies decreasing as green leaf nutrient concentrations increased. However, specific patterns of resorption and the functional relationships between nutrient concentrations in green and senesced leaves varied by nutrient and plant functional group. Functional relationships between N concentrations in green and senesced leaves were indistinguishable between the dominant groups, suggesting that variation in N resorption efficiency was largely the result of inter-life form differences in green leaf N concentrations. In contrast, observed differences in P resorption efficiencies between life forms appear to be the result of both differences in green leaf P concentrations as well as inherent differences between life forms in the fraction of green leaf P resorbed from senescing leaves. Our results indicate that foliar N:P ratios are poor predictors of resorption efficiency in this ecosystem, in contrast to N and P resorption proficiencies, which are more responsive to foliar N:P ratios.     

江西阳际峰30种阔叶树叶片氮磷含量及再吸收效率

养分再吸收是植物养分利用的重要策略,体现了植物对养分留存、利用和适应环境的能力.为研究亚热带不同生活型(常绿与落叶)阔叶树养分含量与养分再吸收的关系,以江西阳际峰国家级自然保护区内30种阔叶树为研究对象,测定成熟和衰老叶片氮(N)和磷(P)含量,分析常绿和落叶树种叶片N和P含量及其再吸收效率差异,揭示阔叶树种叶片养分再...     

氮添加对黄河三角洲滨海湿地芦苇养分再吸收效率的影响

大气氮沉降增加能改变土壤养分可利用性,影响滨海湿地植物的养分再吸收。目前研究多关注氮沉降量对养分再吸收过程的影响,且研究集中于叶片,鲜有研究区分不同形态氮素对植物不同器官养分再吸收过程的影响。通过两年的野外控制实验,研究硝态氮、铵态氮添加对黄河三角洲滨海湿地芦苇(Phragmites australis)叶、茎养分再吸收效率的影响。结果表明：两类氮添加均显著增加叶、茎的氮、磷含量(P<0.001),增幅达32.74%—43.22%(氮)、30.91%—36.51%(磷)。叶片氮的再吸收效率为54.14%—67.66%,茎氮的再吸收效率为50.60%—62.85%。叶片磷的再吸收效率为56.80%—70.38%,茎磷的再吸收效率为77.43%—84.95%。两类氮添加均显著降低氮、磷的再吸收效率(P<0.001),但两类氮添加处理下的养分再吸收效率无差异。叶、茎氮的再吸收效率无差异,但茎磷的再吸收效率明显高于叶(P<0.01)。总之,氮添加降低芦苇对氮、磷的再吸收效率,且茎对养分的再吸收也具有不可忽略的贡献。     

重庆石灰岩地区主要木本植物叶片性状及养分再吸收特征

以重庆石灰岩地区15种常绿木本植物和14种落叶木本植物为研究对象,对两种生活型植物叶片衰老前后叶干物质含量(LDMC)、比叶面积(SLA)和叶片厚度(LT)进行了比较,并采用不同的计算方法(单位质量叶片养分含量、单位面积叶片养分含量)分析了两类植物叶片衰老前后养分含量及再吸收特征,最后对养分再吸收效率与其他叶性状因子之间的关系进行了相关分析。结果表明:常绿植物成熟叶LDMC、LT及衰老叶LT显著低于落叶植物,落叶植物成熟叶和衰老叶SLA均显著高于常绿植物(P0.05);基于单位质量叶片计算的养分含量,常绿植物成熟和衰老叶N、P量均低于落叶植物,而基于单位面积叶片计算的N、P含量则表现出相反的趋势;基于不同方法计算的N、P再吸收效率差异不明显,其中常绿植物基于单位质量叶片养分含量计算的N、P平均再吸收效率为39.42%、43.79%,落叶植物的为24.08%、33.59%;常绿和落叶植物N、P再吸收效率与LDMC、SLA、LT和成熟叶N、P含量之间没有显著相关性,但与衰老叶养分含量存在显著负相关(P0.05)。研究发现,无论是常绿植物还是落叶植物,衰老叶N、P含量均较低,表明石灰岩地区植物具有较高的养分再吸收程度。     

天童常绿阔叶林若干树种的叶片营养转移研究

对天童国家森林公园 1 8种植物在落叶前后营养转移量的研究表明 ,不同植物的营养转移率不尽相同 ,N的平均转移率为 3 7.86% ,标准偏差 1 0 .67% ;P的平均转移率为 44.76% ,标准偏差 1 5 .40 %。经方差分析 ,N、P转移率无明显差异 (s=0 .1 3 8)。同时 ,P的转移率与植物成熟叶中的P含量及N/P存在正相关 ,而N的转移率与植物成熟叶子的N含量和N/P不相关。另外 ,常绿植物的N转移率平均值是 3 5 .74% (标准差9.46% ) ,落叶植物N转移率平均值是 3 8.72 % (标准差 1 2 .65 % ) ;常绿植物的P转移率平均值是 3 7.72 % (标准差 1 3 .0 0 % ) ,落叶植物P转移率平均值是 5 5 .3 7% (标准差 1 5 .5 4% )。对落叶和常绿阔叶二种生活型植物进行ANOVA分析 ,表明N转移率无明显差异 ,而P转移率有差异 (P <0 .0 5 )。