Amplitude abnormalities in the scalp far-field N18 of SSEPs to median nerve stimulation in patients with midbrain-pontine lesion

Various amplitude ratios were measured in 20 normal controls and 36 patients with midbrain-pontine, thalamic or putaminal lesions in order to evaluate the amplitude abnormalities in scalp far-field N18 following median nerve stimulation. A study of normal controls showed that the distributions of P9/N18, P14/N18 and N18/P14 + N18 resembled a gaussian distribution and could be used as criteria for determining the decrease in N18 amplitude in each patient. There was a decrease in N18 amplitude, or the absence of N18, in patients with midbrain-pontine lesions, but not in those with thalamic or putaminal lesions.Nine amplitude ratios (P11/P9, P14/P9, N18/P9, P9/P11, P9/P14, P9/N18, N18/P14, P14/N18 and N18/P14 + N18) were compared statistically for normal controls and 3 groups of patients based on non-parametric, Wilcoxon's non-pairs and signed-rank tests. A decrease in N18 amplitude in midbrain-pontine lesion was shown by significant changes in N18/P9, P9/N18, N18/P14, P14/N18 and N18/P14 + N18, no amplitude decreases in P11 and P14 being found from the amplitude ratios of P11/P9, P9/P11, P14/P9 and P9/P14. No significant changes were seen in any of the 9 amplitude ratios when the normal controls and patients with thalamic and putaminal lesions were compared.The amplitude ratios of N18 can be used to detect a decrease in N18 amplitude in patients with midbrain-pontine lesions. The data obtained support the hypothesis that N18 originates in the midbrain-pontine region and that neither the thalamus nor thalamocortical radiation make major contributions to the formation of the N18 peak.     

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。     

喀斯特区不同退化程度植被群落植物-凋落物-土壤-微生物生态化学计量特征

为摸清喀斯特植被退化对群落各组分C、N、P生态化学计量特征及内稳态特征的影响，为喀斯特退化生态系统植被恢复与重建提供科学依据，以桂西北喀斯特地区5种退化程度植被群落为研究对象，测定了不同退化程度植被群落植物叶片、凋落物、土壤和微生物生物量的C、N、P含量，分析其化学计量比特征、相互关系及植物内稳性特征。结果表明：(1)随着退化程度加剧，叶片C、N、P含量、N∶P和凋落物N∶P、微生物量C显著下降，而叶片C∶N、C∶P则显著增加，且植物叶片N∶P<14;随退化程度加剧，凋落物N、P含量、土壤C、N、P含量、微生物量N、P呈先略有增后显著降低的趋势，且不同退化程度群落土壤N∶P和微生物量C∶N无显著差异。(2)叶片N、P含量与土壤N、P含量，叶片C∶P与土壤C∶N、C∶P、N∶P,叶片N∶P与凋落物N、N∶P,叶片C、N、P含量与微生物量C呈显著或极显著正相关关系；叶片C∶N与土壤C、N,叶片C∶P与土壤N、P,叶片N∶P与土壤P呈显著或极显著负相关关系。(3)喀斯特地区植物叶片N、P元素的内稳性指数(H)平均值分别为2.74和2.31,属于弱稳态型，叶片N∶P的H值为5.14,为稳...     

氮磷添加对荒漠草原植物-凋落物-土壤生态化学计量特征的影响

为明确植物、凋落物和土壤养分含量及化学计量比对土壤中添加多种限制性养分的响应,阐明“植物-凋落物-土壤”连续体化学计量动态及各组分之间的协同作用,以宁夏荒漠草原为研究对象,于2018年开始进行氮(N)、磷(P)养分添加控制试验。试验处理包括对照(CK)、N添加、P添加、NP共同添加4个处理。结果表明：(1)NP共同添加显著增加了荒漠草原植物N和P含量、以及凋落物和土壤P含量,显著降低了荒漠草原植物C∶N和C∶P、以及土壤和凋落物C∶P和N∶P。P添加显著增加了荒漠草原植物、凋落物和土壤P含量,显著降低了植物、凋落物、土壤C∶P和N∶P。N添加分别增加了植物、凋落物N含量和N∶P,但对植物N含量影响未达到显著水平。(2)C、N、P含量和N∶P大小均表现为植物>凋落物>土壤,C∶N和C∶P均表现为凋落物>植物。(3)N添加提高了荒漠草原植物对P再吸收效率,降低了荒漠草原植物对N利用效率;P添加提高荒漠草原植物对N再吸收效率,降低荒漠草原对P的利用效率;NP共同添加提高了荒漠草原植物对N和P再吸收效率,降低了荒漠草原植物对N和P利用效率。(4)植物-凋落物-土壤的N、P含量...     

Nitrogen (N) Deposition Impacts Seedling Growth of Pinus massoniana via N:P Ratio Effects and the Modulation of Adaptive Responses to Low P (Phosphorus)

Background

In forest ecosystems with phosphorus (P) deficiency, the impact of atmospheric nitrogen (N) deposition on nutritional traits related to P uptake and P use potentially determines plant growth and vegetation productivity.

Methodology/Principal Findings

Two N deposition simulations were combined with three soil P conditions (homogeneous P deficiency with evenly low P; heterogeneous P deficiency with low subsoil P and high topsoil P; high P) using four full-sib families of Masson pine (Pinus massoniana). Under homogeneous P deficiency, N had a low effect on growth due to higher N:P ratios, whereas N-sensitive genotypes had lower N:P ratios and greater N sensitivity. The N effect increased under higher P conditions due to increased P concentration and balanced N:P ratios. An N:P threshold of 12.0–15.0 was detected, and growth was increased by N with an N:P ratio ≤ 12.0 and increased by P with an N:P ratio ≥ 15.0. Under homogeneous P deficiency, increased P use efficiency by N deposition improved growth. Under heterogeneous P deficiency, a greater P deficiency under N deposition due to increased N:P ratios induced greater adaptive responses to low P (root acid phosphatase secretion and topsoil root proliferation) and improved P acquisition and growth.

Conclusions/Significance

N deposition diversely affected seedling growth across different P conditions and genotypes via N:P ratio effects and the modulation of adaptive responses to low P. The positive impact of N on growth was genotype-specific and increased by soil P addition due to balanced N:P ratios. These results indicate the significance of breeding N-sensitive tree genotypes and improving forest soil P status to compensate for increasing N deposition.     

Variations in leaf and root stoichiometry of Nitraria tangutorum along aridity gradients in the Hexi Corridor,northwest China

Nitrogen (N) and phosphorus (P) concentrations and N: P ratios between leaves and roots of Nitraria tangutorum along aridity gradients were studied. N. tangutorum was relatively limited by N in April (mean leaf N: P ratio = 11.13) and by P in August (mean leaf N: P ratio = 38.78). N and P in both leaves and roots were highly correlated across sampling sites. In April both leaf and root N and P concentrations increased along aridity gradients. Mean leaf N: P ratios changed slightly, but mean root N: P ratios increased with increasing aridity gradients. We suggest that leaf N: P ratios can indicate nutrient status at different plant growth stages, and root N: P ratios can signify if the amount of soil nutrients is insufficient.     

Interspecific interactions affect N and P uptake rather than N:P ratios of plant species: evidence from intercropping

种间相互作用影响植物氮和磷的吸收量而不是氮磷比 量化不同农艺措施下作物氮和磷吸收量(即从农田中移除的量)的化学计量特征对理解农田生态系统中的养分收支和优化氮、磷肥施用至关重要。目前还不清楚在不同的氮肥和覆膜措施下,单作和间作体系作物氮和磷吸收量以及氮磷化学计量特征随整个生长季的变化。本研究探讨了植物种间养分竞争如何对(1) 5种种植模式(小麦、玉米和大麦单作、小麦/玉米和大麦/玉米间作),(2)两种施氮水平(0和225 kg N ha⁻¹)和(3)两种玉米覆膜处理(覆膜和不覆膜)下的作物氮、磷吸收量(以及氮磷比)时间动态的影响。研究结果表明,小麦和大麦的氮、磷竞争能力强于玉米,导致间作体系共生期的小麦和大麦氮、磷吸收量相比于单作增加,而玉米氮、磷吸收量相比于单作减少。3种作物植株氮磷比随作物生长而降低。作物氮磷比不受间作的影响,也不随施氮呈现一致的变化,覆膜降低了玉米的氮磷比。两种间作体系群落水平的氮磷比在成熟期与相应单作不同。由于(1)间作从土壤移除的氮和磷的比例不同于单作,以及(2)作物对氮和磷的吸收在施氮和覆膜下均是不耦合的,这些发现可能对间作系统的养分收支有启示意义。     

施用氮、磷肥对作物体内养分含量的影响

２年四季盆栽试验结果表明：（１）施用磷肥能改善作物地上部生物学产量向籽粒分配．在Ｎ、Ｐ胁迫条件下,施Ｎ增加非经济产量与经济产量比值．（２）对于谷子,在Ｎ、Ｐ亏缺条件下,施Ｎ能增加茎叶含Ｎ量,降低Ｎ向籽粒中转移;施磷能改善Ｎ在茎叶与籽粒之间的分配。（３）对于小麦,在Ｎ或Ｐ胁迫条件下,补施Ｐ或Ｎ均能增加冠根吸Ｎ量之比,对于谷子,其对冠根吸Ｎ量之比影响与小麦完全不同．（４）谷子在Ｎ、Ｐ胁迫条件下,施Ｎ能降低Ｐ在籽粒中积累,施Ｐ却能显著地改善磷向籽粒中转移,小麦在Ｎ、Ｐ胁迫条件下,增施Ｐ或Ｎ均能显著改善磷向籽粒中转移。     

Vegetation in contrasting soil water sites of upland herbaceous grasslands and N:P ratios as indicators of nutrient limitation

Effects of differences in long-term water supply were examined on soil characteristics, primary production and species composition in a wet and a dry site of an upland herbaceous grassland. Also the responses of species to N and P enrichments were examined. N and P concentrations of non-legume species were positively related, indicating that biomass N:P ratios seem to be mainly determined by N:P supply ratios. Forbs had generally higher concentrations than graminoids. Intermittent water inundation of soil in the wet site resulted in greater soil N and P availability. The greater productivity of this site promoted the growth of forbs. A fertilizer experiment showed that biomass was limited by N only in the wet site, but by both nutrients in the dry one. The species with the higher N and P concentrations were favored more after N and P enrichment, respectively; however, species enhancement was not related to N:P ratios of species. This indicates that N and P concentrations of species, rather than N:P ratios of species, are better predictors of species responses to N and P enrichment. N:P ratios of whole communities were 8.73 for the wet and 11.36 for the dry site. These values in comparison with the responses of plant communities to N and P fertilization show that thresholds of N:P ratios indicative of N or P limitation are much lower than those found for European wetlands.     

湘西南石漠化地区灌丛植物叶N、P化学计量特征

以湘西南石漠化地区灌丛植物叶片为研究对象,分析了不同功能群植物以及3种不同石漠化程度(轻度、中度、重度)下植物叶片N、P化学计量特征.结果表明: 湘西南石漠化地区常见植物叶片平均N含量为12.89 g·kg^-1,P含量为1.19 g·kg^-1,N/P值为11.24,大部分植物生长受到N的限制.不同生活型之间植物叶片N含量为落叶灌木>常绿灌木>一年生草本>多年生草本,P含量与N/P值为落叶灌木>多年生草本.不同科植物之间叶片N、P含量和N/P值差异显著,禾本科植物叶片N、P含量最低,与其他科植物共同受N限制;豆科植物叶片N含量和N/P值最高,主要受P限制.双子叶植物与C3植物叶片N、P含量分别高于单子叶植物与C4植物,N/P值差异均不显著.固氮植物叶片N含量以及N/P值均高于非固氮植物,P含量差异不显著.各样地中植物叶片N、P含量之间的相关性显著,N/P值与N含量的相关性显著,仅与中度石漠化样地P含量差异显著.不同石漠化程度之间植物叶N、P含量以及N/P值差异不显著.     

氮沉降和经营强度对毛竹林凋落叶生态化学计量特征的影响

为探讨氮沉降和经营强度对毛竹凋落叶化学计量特征的影响,研究了不同强度模拟氮沉降(低氮: 30 kg N·hm^-2·a^-1;中氮: 60 kg N·hm^-2·a^-1;高氮: 90 kg N·hm^-2·a^-1)对两种经营强度(粗放经营和集约经营)毛竹林凋落叶生态化学计量特征的影响.结果表明: 相比于粗放经营,集约经营使毛竹凋落叶C、N、P含量分别显著提高9.3%、32.4%和22.7%, 而C∶N、C∶P和N∶P分别显著降低17.4%、54.3%和44.6%.粗放经营条件下,低、中氮沉降显著提高了毛竹凋落叶C、N、P含量,但显著降低了C∶N、C∶P和N∶P;高氮沉降显著提高了C、N含量及C∶P、N∶P,但显著降低了P含量.集约经营条件下,低氮沉降显著提高了毛竹凋落叶P含量,降低了C含量及C∶P、N∶P;中氮沉降显著提高了N、P含量,降低了C含量及C∶N、C∶P和N∶P;高氮沉降显著提高了C∶N、C∶P和N∶P,降低了P含量.经营方式和氮沉降的交互作用显著影响了凋落叶除C∶N以外的生态化学计量特征.毛竹凋落叶P与土壤P含量呈显著相关.     

氮磷添加对麦冬根部养分浓度及其化学计量比的影响

以城市地被植物麦冬(Ophiopogon japonicus(Thunb.)Ker-Gawl.)为研究对象,研究了土壤中添加氮(N)磷(P)后对植物根部N、P养分及其化学计量比的影响。结果表明,实验监测期间(10-12月),麦冬根部N浓度平均值表现为N(5gm-2) P(1gm-2)处理>N(5gm-2)处理=P(1gm-2)处理>对照,根部P浓度和N:P比差异不显著(P>0.1)。而监测期间的N、P月份动态结果表明,同对照相比,N处理、P处理和N P处理的麦冬根部N、P浓度和N:P比的差异性均表现为监测前期(10月)较大,中后期(11-12月)较小的变化趋势。这说明麦冬能保持其根部N、P水平的稳定性,具有较强的应对N沉降的能力,且补充P肥可增强这种能力。因此,麦冬可在大气沉降严重的地区应用和推广。     

太平洋中西部海域浮游植物营养盐的潜在限制

2009年8月至9月期间在太平洋西部N1站和中部N2站进行现场营养盐加富培养实验。结果显示:N1站,浮游植物生物量对N或者P添加都有较强的响应,其中N+P+Si组和N+P组浮游植物长势迅速,叶绿素a从初始的0.03μg/L分别达到2.12μg/L和1.83μg/L,同时P先于N和Si之前被耗尽;说明N1站为N、P共同限制,P是首要限制因子。而N2站,浮游植物生物量仅对N、P共同添加有明显响应,N先于P和Si被浮游植物消耗殆尽。利用培养过程中营养盐比值变化推断,N1站浮游植物以低于Redfield ratio(16N∶1P)吸收N和P;而N2站浮游植物以高于Redfield ratio(16N∶1P)吸收N和P。这可能解释了太平洋西部的寡营养盐海域为潜在P限制,而在太平洋中部海域则为潜在N限制。     

P30 and N33 of posterior tibial nerve SSEPs are analogous to P14 and N18 of median nerve SSEPs

Generator sources of far-field P30 and N33 components produced bosterior tibial nerve stimulation were compared with those of the P14 and N18 components of median nerve stimulated somatosensory evoked potentials. Intracranial spatio-temporal distributions of P30 and N33 were similar to those of the P14 and N18 obtained by median nerve stimulation. In clinical cases, the changes in P30 and N33 were correlated with those in P14 and N18, indicative that P30 and N33 are derived from activities similar to those that produce P14 and N18.     

Effects of different nitrogen:phosphorus levels on the growth and ecological stoichiometry of Glycyrrhiza uralensis北大核心CSCD

Aims The increase in atmospheric nitrogen (N) deposition has accelerated N cycling of ecosystems, probably resulting in increases in phosphorus (P) demand of ecosystems. Studies on the effects of artificial N:P treatment on the growth and carbon (C), N, P ecological stoichiometry of desert steppe species could provide not only a new insight into the forecasting of how the interaction between soils and plants responses to long-term atmospheric N deposition increase, but also a scientific guidance for sustainable management of grassland in northern China under global climate change. Methods Based on a pot-cultured experiment conducted for Glycyrrhiza uralensis (an N-fixing species) during 2013 to 2014, we studied the effects of different N:P supply ratios (all pots were treated with the same amount of N but with different amounts of P) on aboveground biomass, root biomass, root/shoot ratio, and C:N:P ecological stoichiometry both in G. uralensis (leaves and roots) and in soils. Additionally, through the correlation analyses between biomass and C:N:P ecological stoichiometry in leaves, roots, and soils, we compared the differences among the C:N:P ecological stoichiometry of the three pools, and discussed the indication of C:N:P ecological stoichiometry in soils for the growth and nutrient uptake of G. uralensis. Important findings The results showed that, reducing N:P decreased C:P and N:P ratios both in G. uralensis (leaves and roots) and in soils but increased aboveground biomass and root biomass of G. uralensis, indicating that low to moderate P addition increased P availability of soils and P uptake of G. uralensis. However, excessive low N:P (high P addition) led to great decreases in soil C:P and N:P ratios, thus hindering N uptake and the growth of G. uralensis. C:N:P ratios in the two pools of G. uralensis (especially in leaves) had close correlations with soil C:N:P ratio, indicating that the change in soil C:N:P ratio would have a direct influence on plants. Our results suggest that, through regulating C:N:P ratio in leaves and soils, appropriate amounts of P addition could balance soil P supply and plant P demand and compensate the opposite influences of long-term atmospheric N deposition increase on the structure of desert steppe.     

氮添加对武夷山亚热带常绿阔叶林植物叶片氮磷化学计量特征的影响

该文以福建武夷山亚热带常绿阔叶林为研究对象, 通过设置3个氮(N)添加梯度的野外实验, 研究了群落内乔木植物、灌木植物、草本植物、蕨类植物和苔藓植物叶片N、磷(P)化学计量特征对N沉降的响应, 以及不同功能群和物种化学计量特征对N沉降响应的差异。在已开展5年人工N添加的样地内, 3年的监测结果表明: N添加整体上提高了植物叶片N含量, 草本层植物叶片N含量对N添加的响应比乔木层和灌木层植物更加敏感, 优势种米槠(Castanopsis carlesii)、草本植物砂仁(Amomum villosum)、蕨类植物狗脊(Woodwardia japonica)的叶片N含量显著增加。N添加整体上增加了植物叶片P含量, 乔木层植物和灌木层植物叶片P含量没有显著变化, 草本层植物叶片P含量显著增加, 而苔藓植物叶片P含量显著减少。N添加促使武夷山亚热带常绿阔叶林植物叶片N:P由18.67上升至19.72, 加剧了植物生长的P限制; 乔木物种N:P的变化较灌木和草本物种更加稳定。N添加条件下, 植物叶片N:P的变化主要受到叶片P含量而非N含量变化的影响, N添加对生态系统P循环的影响显著。     

阿拉善荒漠区6种主要灌木植物叶片C:N:P化学计量比的季节变化

为了解同一生活型不同种植物叶片碳(C)、氮(N)、磷(P)生态化学计量学特征随季节变化的响应规律,在生长季不同月份,对阿拉善荒漠区6种主要灌木植物霸王(Zygophyllum xanthoxylum)、白刺(Nitraria tangutorum)、红砂(Reaumuria soongorica)、驼绒藜(Ceratoideslatens)、猫头刺(Oxytropis aciphylla)、沙冬青(Ammopiptanthus mongolicus)的物候期进行了连续的观察,并采集植物叶片,分析了其C、N、P含量及计量比在不同月份的变化.结果显示:1)同一生活型的6种植物的叶片C、N、P及C:N、C:P和N:P在整个生长季内的变化规律不同,且以上各指标季节间的变异系数在6种植物之间也存在差异;2)单个植物种叶片C、N、P含量及其计量比的季节变异分析显示,叶片C、N含量及C:N的季节变异较小,叶片P含量及C:P和N:P的季节变异较大,6种植物叶片C、N含量及C:N由于季节变异所计算的变异系数变化范围分别为0.60％-10.20％、6.09％-20.50％和5.87％-18.78％,6种植物叶片P含量的季节变异所产生的变异系数范围为16.43％-43.43％,叶片C:P和N:P的变异系数范围分别为8.48％-31.95％和11.86％-40.73％;3)综合分析6种植物叶片C、N、P及其计量比各指标在整个生长季节内的变异,变异系数由大到小排序为:P(28.85％)＞C:P(25.02％)＞N:P(22.18％)＞N(14.22％)＞C:N(12.48％)＞C(4.62％);4)生长季节与植物种类对植物叶片C、N、P及其计量比影响的交叉分析显示,植物叶片C、N含量的变异主要受植物种类影响,植物叶片P含量的变异主要受生长季节影响,植物叶片C:N、C:P和N:P的变异都主要受植物种类影响.     

喀斯特峰丛洼地不同森林类型植物和土壤C、N、P化学计量特征

研究西南喀斯特峰丛洼地人工林、次生林、原生林3个不同森林类型的6个代表性植物群落C、N、P化学计量特征及其与土壤的关系.结果表明: 不同森林类型植物和土壤C、N、P含量均存在显著差异.土壤C和N含量均为次生林最高,人工林最低,土壤P含量为人工林最高,原生林最低;植物C和P含量变化趋势为人工林>原生林>次生林,植物N含量为次生林最高,原生林最低.土壤C∶P、N∶P以及植物C∶P均为原生林显著高于次生林和人工林,土壤C∶N在不同森林类型间差异不显著;植物N∶P为次生林最高,人工林最低,植物C∶N为原生林>人工林>次生林.在不同森林类型中,乔木叶片N含量与P含量、C∶N与C∶P以及C∶P与N∶P之间均呈显著线性正相关,除了植物叶片C∶N与N∶P以及土壤C∶N与N∶P之间呈显著线性负相关外,植物和土壤的C、N、P、C∶P均无显著相关性,说明土壤C、N、P供应量对乔木叶片C、N、P含量影响不大.     

华北石质山地侧柏人工林C、N、P生态化学计量特征的季节变化

以北京九龙山自然保护区幼龄侧柏人工林为研究对象,对其不同生长季节叶、枝、根(0—10 cm、10—20 cm土层)的碳(C)、氮(N)、磷(P)含量及其生态化学计量学特征进行了分析,深入探讨了生长季节与器官以及两因素交互作用对以上特征的影响,研究有助于理解植物各性状之间的相互作用以及植物生长过程中资源的利用和分配状况。结果表明:1)不同器官间C含量为414.97—461.58 g/kg,枝最大,根(0—10 cm)最小;N含量为6.57—14.28 g/kg,叶最大,枝最小;P含量为0.39—1.28 g/kg,叶最大,根(10—20 cm)最小;C∶N为31.76—70.98,枝最大,叶最小;C∶P为369.93—1099.20,根(10—20 cm)最大,叶最小;N∶P为9.21—23.81,根(0—10 cm)最大,枝最小。整个生长季节中侧柏各器官C含量最稳定,变异系数均小于7%;P含量变异性最大,变异系数均超过15%,N含量变异性介于两者之间;各器官中C∶N和N∶P较C∶P更为稳定,C、N与P具有较好的耦合协同性,C∶P和N∶P的变化主要取决于P的变化。2)器官对C、N、P含量及其化学计量关系均存在显著影响,生长季节对N和P含量存在显著影响,两者交互作用只对P含量存在显著影响,器官对侧柏C、N、P含量及其化学计量变异的贡献大于生长季节。3)侧柏各器官间C、N、P含量及其化学计量比相关性多数未达到显著性水平,仅有叶与枝中的P及C∶P显著相关,说明侧柏器官分化过程中各器官对元素的吸收利用具有特异性。侧柏叶片N∶P14,说明生长季节里幼龄侧柏人工林更多受到N限制。     

Impacts of nitrogen addition on foliar nitrogen and phosphorus stoichiometry in a subtropical evergreen broad-leaved forest in Mount Wuyi

Aims Our purpose was to explore the effects of nitrogen addition on foliar nitrogen (N), phosphorus (P) and N:P stoichiometry and to assess their differences among different species and functional groups.
Methods N addition experiment has been conducted in a subtropical evergreen broad-leaved forest in Mount Wuyi, Fujian Province since 2011. Foliar concentrations of nitrogen and phosphorus were measured and foliar stoichiometry was estimated in tree, shrub, herb, fern and moss species following the N addition treatments from 2013 to 2015.
Important findings Generally, foliar N increased for almost all species and herbaceous plants are much more sensitive than trees and shrubs under N addition. Foliar N of Castanopsis carlesii, Amomum villosum, Woodwardia japonica increased significantly under N addition. Foliar P for most species was sensitive to the N addition. Foliar P of herbaceous plants increased significantly but foliar P of Leucobryum chlorophyllosum decreased significantly. The results showed the subtropical evergreen forest in Mount Wuyi was mainly limited by P and mean foliar N:P ratios enhanced from 18.67 to 19.72 under N addition, indicating that the strength of P limitation was enhanced by N addition. N:P ratios of the dominant arboreal species in the communities tended to be stable, while N:P ratios of herbaceous plants and shrubs increased. The changes in N:P ratios were mainly determined by P dynamics instead of N dynamics under N addition, and our results confirmed that increasing N availability can affect P cycling.