Plant trait responses to variation in N and P availability

Global change drivers such as eutrophication and plant invasions will create novel environments for many plant species. Through adaptive trait plasticity plants may maintain their performance under these novel conditions and may outcompete those showing low adaptive trait plasticity. In a greenhouse study, we determined if plasticity in traits is adaptive or maladaptive in endangered, non-endangered and invasive plant species in response to variation of nitrogen (N) and phosphorus (P) availability (N:P ratios 1.7, 15 and 135) and whether plastic trait responses are adaptive and/or costly for fitness (i.e. biomass). Species choice comprised 17 species from three functional groups (legumes, non-legume forbs and grasses), either classified as endangered, non-endangered or invasive. After two months plants were harvested and nine traits related to carbon assimilation and nutrient uptake were measured (leaf area, SLA, LDMC, SPAD, RMR, root length, SRL, root surface area and PME activity). We found more traits responding plastically to variation in P than in N. Plasticity only created costs when P was varied. Plasticity in traits was mostly adaptively neutral towards fitness, with plasticity in three traits being similarly adaptive across all species groups: SPAD (as a measure of chlorophyll content, adaptive to N and P limitation), leaf area and root surface area (adaptive to P limitation). We found little differences in trait plasticity between endangered, non-endangered and invasive species. Synthesis. Along a gradient from N limitation, balanced N:P supply and P limitation we found that the type of fluctuating nutrient (i.e. if N or P is varied) is decisive for the adaptive value of a trait. Variation in P availability (from balanced supply to P limitation) created both a stronger reduction in fitness as well as created plasticity costs in more traits than variation in N availability (from balanced supply to N limitation). However, the patterns observed in our study may change if nutrient availability is altered, either by nutrient inputs or by a shift in nutrient availabilities, e.g. by decreasing N input as foreseen by European Legislation, but without simultaneously decreasing P input. Methods The dataset contains plant trait information of 17 annual species (grasses, non-legume forbs, legumes). Plants were raised in a greenhouse and exposed to N (nitrogen) limitation, P (phosphorus) limitation, and a balanced supply of both N and P. After eight weeks, plants were harvested and traits were measured. General information: Family (Poaceae, Onagraceae, Fabaceae), Maturity (all plants mature at time of harvest), Status (plant species considered either invasive, endangered or non-endangered in central Europe), Plant Growth Form (grass, non-legume forb, forb), Life Span (annual), Start experiment (start date for each individual), End experiment (date of harvest for each individual), Treatment (N limitation, balanced nutrient supply, P limitation), total.supply.rate.N.mg (total amount of N supplied to each individual in the course of the experiment, i.e. 121.5mg, 40.5mg, 13.5mg) total.supply.rate.P.mg (total amount of P supplied to each individual in the course of the experiment, i.e. 0.9mg, 2.7mg, 8.1mg), repeats.per.trt (number of repetitions per trt and species, 1–10). Plant species: Avena sterilis, Bromus hordeaceus, Bromus japonicus, Bromus secalinus, Bromus squarrosus, Epilobium anagallidifolium, Epilobium ciliatum, Epilobium fleischeri, Hordeum jubatum, Hordeum murinum, Lolium remotum, Lolium temulentum, Lupinus angustifolius, Medicago lupulina, Trifolium arvense, Trifolium dubium, Trifolium subterraneum Plant traits include: Total Biomass (mg), Total leaf area (mm²), Specific leaf area (SLA, mm2/mg), Leaf dry matter content (LDMC, mg/g), SPAD (measure of chlorophyll content, dimensionless), Root mass ratio (RMR, mg/mg), Total root length (m), Specific root length (SRL, m/mg), Root surface area (cm2), root phosphomonoesterase activity (PME, µmol pNPP /g*h). Measurement for most traits followed Pérez-Harguindeguy, N., et al. (2013). "New handbook for standardised measurement of plant functional traits worldwide." Australian Journal of Botany 61: 167-234.富营养化、植物入侵等全球变化驱动因子将为诸多植物物种塑造全新的生存环境。通过适应性性状可塑性（Adaptive trait plasticity），植物可在这些新环境中维持自身适合度（Fitness），甚至竞争排挤那些适应性性状可塑性较低的物种。本研究依托温室实验，旨在明确濒危、非濒危与入侵植物物种的性状可塑性对氮（N）、磷（P）有效性变化（N:P质量比分别为1.7、15和135）的响应是适应性的还是适应不良的，同时探究性状的可塑性响应对适合度（即以生物量为指标）是否具有适应性或适合度代价。 本研究选取17个物种，隶属于3个功能群（豆科、非豆科草本非禾草与禾本科植物），其濒危等级分别归类为濒危、非濒危或入侵物种。实验处理两个月后收获植株，测定了9项与碳同化及养分吸收相关的性状：叶面积、比叶面积（Specific leaf area, SLA）、叶干物质含量（Leaf dry matter content, LDMC）、SPAD值、根质量比（Root mass ratio, RMR）、总根长、比根长（Specific root length, SRL）、根表面积及磷酸单酯酶活性（Phosphomonoesterase activity, PME）。 研究结果显示，相较于氮有效性变化，更多性状会对磷有效性变化产生塑性响应；且仅当磷有效性发生变化时，可塑性才会带来适合度代价。总体而言，性状可塑性对植物适合度多呈适应性中性，但三类物种群在3项性状上的可塑性均表现出一致性的适应性：作为叶绿素含量测定指标的SPAD值（对氮、磷限制均具有适应性）、叶面积及根表面积（仅对磷限制具有适应性）。此外，濒危、非濒危与入侵物种之间的性状可塑性差异极小。 综合与结论：沿氮限制-养分平衡供给-磷限制的梯度，波动养分的类型（即氮或磷发生变化）是决定性状适应性价值的关键因素。相较于氮有效性变化（从平衡供给转向氮限制），磷有效性变化（从平衡供给转向磷限制）不仅会导致更强的适合度下降，还会在更多性状上引发可塑性代价。不过，若养分供给发生改变——例如通过养分输入调整，或像欧盟立法所预期的那样，仅降低氮输入而不同步减少磷输入，从而改变养分有效性格局，本研究观测到的格局可能会发生变化。 数据集说明 本数据集包含17个一年生植物的性状信息，这些物种隶属于禾草、非豆科草本非禾草及豆科三个功能群。所有植株均在温室中培育，并分别接受氮限制、磷限制及氮磷平衡供给三种处理。培养8周后收获植株并测定相关性状。 通用信息 - 科：禾本科（Poaceae）、柳叶菜科（Onagraceae）、豆科（Fabaceae） - 成熟度：收获时所有植株均已成熟 - 物种状态：在中欧地区被归类为入侵、濒危或非濒危物种 - 植物生长型：禾草、非豆科草本非禾草、草本非禾草 - 寿命：一年生 - 实验起始时间：每个个体的实验开始日期 - 实验结束时间：每个个体的收获日期 - 处理组：氮限制、养分平衡供给、磷限制 - 总氮供给量（total.supply.rate.N.mg）：实验期间供给每个个体的总氮量，分别为121.5mg、40.5mg、13.5mg - 总磷供给量（total.supply.rate.P.mg）：实验期间供给每个个体的总磷量，分别为0.9mg、2.7mg、8.1mg - 每组处理与物种的重复次数（repeats.per.trt）：1~10次 涉及的植物物种： Avena sterilis、Bromus hordeaceus、Bromus japonicus、Bromus secalinus、Bromus squarrosus、Epilobium anagallidifolium、Epilobium ciliatum、Epilobium fleischeri、Hordeum jubatum、Hordeum murinum、Lolium remotum、Lolium temulentum、Lupinus angustifolius、Medicago lupulina、Trifolium arvense、Trifolium dubium、Trifolium subterraneum 测定的植物性状： - 总生物量（Total Biomass，mg） - 总叶面积（Total leaf area，mm²） - 比叶面积（Specific leaf area, SLA，mm²/mg） - 叶干物质含量（Leaf dry matter content, LDMC，mg/g） - SPAD值（叶绿素含量测定指标，无量纲） - 根质量比（Root mass ratio, RMR，mg/mg） - 总根长（Total root length，m） - 比根长（Specific root length, SRL，m/mg） - 根表面积（Root surface area，cm²） - 根磷酸单酯酶活性（root phosphomonoesterase activity, PME，µmol pNPP/(g·h)） 多数性状的测定方法参照Pérez-Harguindeguy N等人2013年发表于《澳大利亚植物学杂志（Australian Journal of Botany）》第61卷的"全球植物功能性状标准化测定新手册（New handbook for standardised measurement of plant functional traits worldwide）"，页码范围167-234。