匍匐茎草本蛇莓克隆构型对土壤养分的可塑性反应

克隆植物构型的可塑性可使它在养分斑块性分布的环境中,相应地调整对土壤养分的获取对策,因而可能具有重要的生态学意义。在一项田间实验中,匍匐茎草本蛇莓(Duchesnea indica Focke）经历了不同土壤养分水平（高、中、低和对照）处理,以研究土壤养分对蛇莓克隆构型的影响。结果表明：随着土壤养分水平的增加,间隔子的长度和分枝角度均逐渐降低,而分枝强度和分株密度增加。在不同养分水平生镜中,蛇莓克隆构型相关特征的可塑性变化可用动态Logistic模型进行模拟和预测,拟合效果较好。结合植物对环境异质性的利用对策,对所揭示的蛇莓克隆构型可塑性进行了讨论。     

天然沸石对土壤保肥性能的影响研究

通过模拟土柱淋洗试验,探讨了沸石对华南地区退化坡地土壤养分保持能力的影响,分析了土柱淋洗后土壤养分的变化,结果表明,在华南地区4种退化坡地土壤上,土柱淋洗液中N和K的含量随着沸石用量水平的增加而下降,不同水平沸石处理的淋洗液中P含量都极低（痕量）,模拟土柱淋洗后土壤中的有效N,有效P和有效K含量随着沸石用量的增加而提高,表明不同水平沸石处理对提高土壤的保肥能力均具有不同程度的促进作用,随着沸石用量的增加,土壤中的无机磷也有不同程度的增加,增加最显著的无机磷形态是铝磷,其次是铁磷,而钙磷和闭蓄态磷则没有明显差异,沸石的 用不会增加土壤淋洗液中硝态氮含量。     

半干旱草地土壤团聚体氮磷转化相关酶活性对氮添加的响应

日益加剧的大气氮沉降对土壤养分循环过程产生了深刻影响,土壤养分转化相关酶是其关键调控途径,而土壤不同粒级团聚体结构和环境差异导致其中酶活性介导的养分转换过程可能不同。但目前对半干旱区土壤团聚体水平养分转化相关酶活性对氮沉降的响应还不清楚。基于黄土高原自然草地持续3年的野外氮添加控制试验,分析不同氮添加水平下土壤不同粒级团聚体中的基础理化性质、氮（亮氨酸氨基肽酶LAP和β-1,4-N-乙酰氨基葡萄糖苷酶NAG）和磷转化相关的酶（磷酸单酯酶PME、磷酸二酯酶PDE和植酸酶phyA）活性及酶计量比,探索氮添加对团聚体酶活性的影响。结果表明：（1）氮添加导致了不同粒级团聚体中pH显著降低;高氮添加引起土壤团聚体有机碳、全氮、硝态氮、C ： P和N ： P升高;（2）随氮添加浓度增加,不同粒级团聚体中PME、PDE和phyA活性先降低后升高,而LAP、NAG和酶活性氮磷比均逐渐升高;团聚体酶活性总体表现为小团聚体（<0.25 mm）>中团聚体（0.25-2 mm）>大团聚体（>2 mm）;（3）在中和大团聚体中氮添加通过影响土壤N相关养分调控P转化相关酶活性。总之,氮添加通过改变团聚体养分及其计量比、pH等影响氮、磷转化相关酶活性。     

芨芨草叶片养分特征对氮磷不同添加水平的响应

植物叶片氮(N)、磷(P)养分特征受土壤可利用性N、P含量和N、P相对比例(N:P)的共同影响, 研究其作用机制有助于解释和评估土壤养分变化对植物养分利用策略的影响。该研究通过盆栽实验, 探讨芨芨草(Achnatherum splendens)养分化学计量学特征和叶片养分回收特征对不同剂量的养分添加(低、中、高3个N添加水平: 1.5、4.5、13.5 g·m^-2·a^-1)及不同土壤N:P (5、15、25)的响应。结果表明: 养分添加水平的提高显著增加了成熟叶片P含量和衰老叶片N、P含量, 显著降低了叶片N、P养分回收效率(NRE, PRE)。土壤N:P的升高显著降低了衰老叶片P含量和叶片NRE, 但增加了成熟和衰老叶片N:P和叶片PRE。相同养分添加水平条件下, 土壤N:P与叶片PRE显著正相关, 但与叶片NRE无显著相关性; 相同N:P条件下, 养分添加水平与NRE负相关, 但与PRE无显著相关性。植物NRE:PRE可以有效地反映环境变化所导致的植物对N、P需求的改变。土壤养分添加水平和N:P共同影响着芨芨草的叶片养分生态化学计量学特征和养分回收。     

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含量和化学计量比之间显著相关，其中植物N、P、N：P与凋落物和土壤N、P、N：P显著正相关，凋落物P、C：N与植物和土壤C：P、N：P显著负相关。（5）荒漠草原植物和凋落物N较稳定（1/H=0.45和1/H=0.48），而植物和凋落物P、N：P较敏感（1/H=0.80、0.73和1/H=0.81、0.78）。荒漠草原植物生长受N限制，N添加缓解荒漠草原植物N限制，P添加和NP添加加剧荒漠草原植物N限制，荒漠草原植物通过改变养分利用策略和再吸收利用效率适应土壤中N、P含量的变化。     

三峡消落带不同坡度狗牙根及实生土壤生态化学计量特征

三峡库区消落带反季节水位波动驱使下植物的养分适应策略和内稳态特征研究对消落带植被恢复及生态功能调控有重要意义。然而,三峡消落带范围广、地形复杂,不同生境下植物适应特征仍存在不确定性。本研究以三峡消落带广泛分布的优势植物狗牙根为研究对象,选取28个地形差异较大的样地进行采样分析,重点探讨不同坡度（0-5°、5-10°、10-15°、15-20°、>20°）狗牙根及其实生土壤生态化学计量特征的变异关系,揭示坡度对狗牙根养分适应及内稳态的影响机制。结果表明：（1）坡度对狗牙根实生土壤的养分及化学计量特征具有显著影响,土壤有机碳（SOC）、全氮（STN）、速效氮（SAN）、全磷（STP）、速效磷（SAP）含量均随坡度增加而降低,<10°的缓坡消落带土壤养分显著高于10°以上的样地;土壤碳氮比（C ∶ N）、碳磷比（C ∶ P）均随坡度增加而降低,而氮磷比（N ∶ P）比相对稳定,表明坡度增大,土壤营养物的流失具有同步性,且流失速度较有机碳慢;（2）随坡度增加,狗牙根各营养器官C含量呈增加趋势,而氮（N）、磷（P）则呈降低趋势,且坡度变化改变了狗牙根各营养器官间的养分分配;植物根、茎C ∶ N、C ∶ P随坡度增加而增加,N ∶ P随坡度增加而降低,而叶片均没有明显变化,表明在坡度改变了土壤养分供应水平的情况下,狗牙根优先稳定其叶片化学计量比以提高适应能力;（3）坡度与土壤中SOC、STN、SAN含量呈现显著负相关,而土壤STN与狗牙根植物养分及化学计量特征均有显著相关关系,由此可见,坡度变化导致土壤氮素流失增加是影响狗牙根生态化学计量特征分异的主要机制;（4）狗牙根与实生土壤的碳氮磷元素内稳性整体表现为C>P>N,化学计量比内稳性表现为C ∶ P>C ∶ N>N ∶ P,随着坡度增加,狗牙根N、P的内稳性呈增强趋势,而C ∶ N、N ∶ P呈显著降低,表明坡度变化导致狗牙根形成了不同的适生策略。研究表明,在三峡库区复杂的地形条件下,狗牙根能有效维持体内化学计量平衡以响应不同的坡度条件,并且内稳性较好,是三峡库区消落带植被恢复与保护的优势植物物种。     

入侵植物南美蟛蜞菊和本土蟛蜞菊生长对土壤养分的响应

植物入侵对全球生态系统造成了严重威胁,土壤养分条件(养分水平和养分异质性)对外来植物的成功入侵有重要影响。为了探讨土壤养分条件对入侵植物与同属本地植物生长的影响,本研究以入侵植物南美蟛蜞菊(Wedelia trilobata)和同属本地种蟛蜞菊(W.chinensis)为试验材料开展了温室控制实验。实验设置了低、中、高及异质性养分条件下的单种和混种两种种植方式,测定了每种植物总生物量,根、茎、叶生物量及分节数、根冠比等指标,并分析了土壤养分对二者生长的影响。结果表明:土壤养分水平增加显著促进了南美蟛蜞菊和本地蟛蜞菊的生长;土壤养分异质性显著增加了南美蟛蜞菊根生物量和根冠比,显著增加了本地蟛蜞菊的总生物量、根生物量和茎生物量;土壤养分水平和养分异质性对南美蟛蜞菊和本地蟛蜞菊的竞争响应均无显著影响;在土壤养分较高或较低时南美蟛蜞菊更容易入侵成功;在异质养分环境中,当南美蟛蜞菊生长处于高养斑块时更容易入侵成功。     

遮光胁迫下外源NO对盆栽长春花土壤养分含量及幼苗生长特征的影响

为探究遮光胁迫下施加外源NO供体（硝普钠,SNP）对土壤养分变化和长春花（Catharanthus roseus）幼苗生长的影响,设置4种处理（全光照生长为对照、外施SNP、遮光、遮光+外施SNP联合处理）,分析盆栽土壤中C、N、P养分含量和土壤理化指标,测定幼苗的株高、节间距、茎直径、叶长、叶宽、叶面积、全株鲜（干）质量。结果表明：遮光和外施NO联合处理下,土壤含水量、土壤pH和土壤有机碳含量显著增加（P<0.05）,而土壤中全氮、碱解氮、全磷和速效磷含量增加但不显著,土壤C/N和C/P值升高,且C/N值达到显著水平（P<0.05）;相关性分析结果表明：土壤pH与有机碳含量呈显著正相关性（P<0.05）,土壤有机碳含量与株高、叶片鲜质量之间呈显著正相关（P<0.05）。说明施加外源NO能促进遮光胁迫下土壤pH升高,改变土壤中有机碳含量,增加C/N值,改善土壤肥力,促进叶片生长发育,增加长春花的生物量,为长春花的科学平衡施肥和生物碱含量的积累提供一定依据。     

亚热带常绿阔叶林不同土壤和林冠环境下蝴蝶花的克隆可塑性

对黄壤和喀斯特土壤两种土壤类型的森林内部和林窗中蝴蝶花的生长指标进行调查,研究异质生境下蝴蝶花的克隆可塑性.结果表明:蝴蝶花在黄壤生境中的分株高度、分株基径和根茎直径均高于喀斯特土壤生境,而分株密度低于喀斯特土壤生境.光照显著影响分株密度,在同一光照条件下土壤质地对分株密度没有显著影响.喀斯特森林内部蝴蝶花的花蕾数及开花数为0,这可能解释为光照和土壤质地双重压力下蝴蝶花对资源摄取和能量分配的权衡与生长维持.在一定程度上,蝴蝶花在黄壤生境中通过增强单个分株的竞争力、减少个体数量来适应环境,趋向K对策,在喀斯特生境中则通过增加个体数量、维持分株竞争力来适应环境,趋向r对策.     

黄土高原刺槐叶片-土壤生态化学计量参数对降雨量的响应特征

以黄土高原10个典型样点的20年刺槐人工林为研究对象,测定了样地中刺槐叶片碳（C）、氮（N）、磷（P）含量,以及0-10 cm和10-20 cm土层土壤的主要理化指标,探讨了黄土高原刺槐叶片-土壤生态化学计量特征参数随水分梯度的变化规律。研究结果发现：①随着降水量增加,刺槐叶C、N含量呈增加趋势,叶片P含量无一致性规律。② 0-10 cm土层中土壤SOC、TN、TP、铵态氮含量以及C ∶ P和N ∶ P均随降雨量增加呈逐渐增加趋势,而C ∶ N比变化不明显。③刺槐叶片C、N、P及其化学计量比与土壤化学计量比相关性较弱,但叶片N、P与土壤铵态氮、速效磷等速效养分含量呈显著正相关（P<0.05）。本研究叶片N ∶ P>16,说明黄土高原刺槐生长主要受P元素限制,且随着降水的增加,土壤P养分的限制加强。     

养分条件对互花米草表型可塑性的影响

通过栽培实验研究了高、中、低不同养分水平对外来入侵种互花米草(Spartina alterniflora)表型可塑性的影响。结果表明:随着养分含量的增加,互花米草分枝强度不断增加,低养分处理与中、高养分处理间差异显著;间隔子长度随着养分含量的增加而增加,但分枝角度不受养分含量的影响;互花米草生物量分配格局显著受养分水平的影响,随着养分的降低,互花米草对地上部分(茎和叶)的生物量投资减小,而对地下部分(根和根茎)的生物量投资增加。这些结果说明,养分水平对互花米草的克隆生长有显著影响,互花米草对不同的养分条件表现出较强的可塑性。     

Root proliferation characteristics of seven perennial arid-land grasses in nutrient-enriched microsites

We compared root proliferation in fertilized microsites among seven cultivars of five commonly planted cool-desert perennial grass species that differ in productivity and competitive ability. In a greenhouse experiment on nutrient-limited plants, one soil microsite in each pot received distilled water (control) and a second microsite received a rich, complete nutrient solution (fertilized). Roots in and adjacent to the microsites were mapped on Mylar windows for 22 days after the injections to determine the magnitude and timing of response in root length relative growth rates (RGRs). Because we provided adequate water, used a high level of fertilization in the treatment microsites, and conducted the experiments during rapid vegetative growth, the results provide a measure of the relative capacities and maximal rates of the grasses responses to enriched microsites. Root samples were harvested from control and fertilized microsites at the end of the experiment to determine the morphological basis of the proliferation response. In all seven grasses fine roots proliferated in the fertilized microsites faster than in the control microsites. The grasses did not differ in the timing of their response which showed a peak 7–8 days after injection. Although one species, Pseudoroegneria spicata cv. Goldar, had higher maximum root length RGR and higher RGR ratio (RGR in fertilized to RGR in control microsites) 7–8 days after injection, the seven grasses did not differ significantly in the magnitude of root length RGR response to fertilizer integrated over the 22 day experiment. The grasses also did not differ significantly in root morphological changes in fertilized mocrosites. Compared to roots in control microsites, roots in fertilized microsites had greater specific root length, length of secondary roots per length of main axis, number of lateral and sublateral roots per length of main axis, and mean lateral root length. Root proliferation was mainly the result of increased lateral branching and lateral root growth in all seven grasses. The consistency of root proliferation responses among these seven cultivars suggests that differences in the capacity for, maximum rate, or morphological basis of root proliferation are not directly related to ecological characteristics such as productivity and competitive ability. Other aspects of root response to nutrient enrichment, such as differential responses as a function of microsite nutrient concentration, plant phenology, plant nutrient status, or specific nutrient element(s), may still be important, but further experiments are required to determine whether different responses to enriched soil microsites among species correspond with know species differences in ecological characteristics.     

Increased nutrient supply facilitates acclimation to high-water level in the marsh plant Deyeuxia angustifolia: The response of root morphology

Both water level and nutrient availability are important factors influencing the growth of wetland plants. Increased nutrient supply might counteract the negative effects of flooding on the growth of the fast-growing species. Experimental evidence is scarce and the mechanism is far from clear. The aim of this study is to identify the role of nutrient availability in acclimation to high-water level by investigating the growth and root morphology of the marsh plant Deyeuxia angustifolia, one of the dominant species in the Sanjiang Plain, China. Experimental treatments included two water levels (0 and 10 cm, relative to soil surface) and three levels of nutrient supply (0, 0.5 and 1 g fertilizer per container). High-water level usually led to decreased biomass accumulation, shoot mass and root mass, whereas biomass accumulation was unaffected by water level at the highest nutrient level, indicating that high-nutrient availability played a role in compensating for the growth loss induced by the high-water level. Increased nutrient supply led to decreased root length in 0 cm water-level treatments, but root length increased with nutrient supply in the 10 cm water-level treatments. High-water level usually led to a lower lateral root density, lateral root:main root length ratio and the diameter of main roots and laterals, whereas increased nutrient supply resulted in thicker main roots or laterals, and a higher total root length, lateral root density and lateral root:main root length ratio. These data indicate that the growth of D. angustifolia is restrained by high-water level, and that increased nutrient supply not only ameliorates root characteristics to acclimate to high-water level but also results in a high-total root length to facilitate nutrient acquisition.     

氮添加对黄河三角洲高潮滩芦苇生长和土壤理化性质的短期效应

氮富集会影响到全球生态系统的植物生长繁殖和土壤理化性质。然而, 目前关于氮富集对潮汐湿地生态系统植物生长和土壤理化性质的影响研究相对较少。通过氮添加野外控制实验, 研究了4个氮添加水平(CK: 0 g·m-2·a-1、N1: 5 g·m-2·a-1、N2: 20 g·m-2·a-1、N3: 50 g·m-2·a-1)对黄河三角洲高潮滩芦苇植被区的芦苇生长和土壤理化性质短期效应。结果表明: N1添加水平显著增加芦苇高度, 增长节间长和叶片宽度, 但减短穗长; N2添加水平显著增加芦苇高度, 增长节间长和叶片长度, 增大叶片宽度, 但减少叶片数; N3添加水平则对芦苇生长繁殖无显著影响。但氮添加对芦苇密度、叶片全碳、全氮和碳氮比的影响不显著。而除了N3添加水平增加了NO3--N (0-10 cm)含量外, 其他土壤理化性质均不受氮添加的影响。因此, 在短期内适量氮输入可促进黄河三角洲高潮滩芦苇的生长, 过量的氮则对其生长没有作用, 保护区应控制对高潮滩芦苇植被过量的氮输入。     

匍匐茎草本蛇莓对基质养分条件的克隆可塑性

A pot experiment with three levels of nutrient (N, P, K) supply was carried out to investigate clonal plasticity of stoloniferous herb Duchesnea indica Focke in response to nutrient availability. The plants had greater biomass at higher levels of nutrient availability. The root/shoot ratio of the plants changed with the nutrient availability in the following order: low level > high level > medium level. They had the largest biomass allocation to stolon at the medium level of nutrient availability. The biomass allocation to petiole did not respond to the treatments. The plants formed more stolons and ramets at the high and medium levels than the low level of nutrient availability. The petiole length, specific petiole weight（mg/cm）and stolon internode length of the plants did not respond to the treatments, while the specific stolon weight (mg/cm）of the plants was greater at the high and medium levels than the low level of nutrient availability. The results have been discussed in the context of adaptation of clonal plants to environmental heterogeneity.     

The influence of different nutrient levels on insect-induced plant volatiles in Bt and conventional oilseed rape plants

Transgenic Bt (expressing the cry1Ac endotoxin gene) and conventional oilseed rape plants grown in different soils were used to study nutrient uptake and emission of volatiles after herbivore damage. All plants were greenhouse-grown in soils representing low-, medium- and high-nutrient levels. The concentrations of N, P, K, Mg and Zn were significantly affected by the transgene, while the main effect of soil type appeared in N, P, Ca, Mg, B, Mn and Zn concentrations in the plants. Plants with four to five leaves were infested with the third instar larvae of Bt-susceptible Plutella xylostella for 48 h, and samples of volatiles were collected and analysed. In the first experiment, the soil nutrient level had a significant effect on the emissions of (Z)-3-hexen-1-ol, (Z)-3-hexenyl acetate, hexyl acetate, (E)-4,8-dimethyl-1,3,7-non-atriene (DMNT), beta-elemene, gamma-bisabolene, alpha-bisabolene and (E)-nerolidol. The induction of these volatiles was significantly higher in infested conventional plants grown at a high-soil nutrient level compared to infested conventional plants at a low-soil nutrient level. In the second experiment, the soil nutrient level had a significant effect on the emissions of (Z)-3-hexen-1-ol, (Z)-3-hexenyl acetate and beta-elemene and, again, this was significantly higher in infested conventional plants grown at high-soil nutrient levels in comparison with infested plants at a low-soil nutrient level. In both experiments, the transgene effect was significant on the emissions of DMNT and (E,E)-alpha-farnesene. The differences in emissions between the two separate experiments suggest that growth conditions (particularly daylength) and sampling procedure may affect the ratio of compounds detected in the emission blend, even though the response to herbivory, nutrient availability and the transgene were similar.     

Community-aggregated plant traits interact with soil nutrient heterogeneity to determine ecosystem functioning

Background and aims

Spatial distribution of soil nutrients (soil heterogeneity) and availability have strong effects on above- and belowground plant functional traits. Although there is ample evidence on the tight links between functional traits and ecosystem functioning, the role played by soil heterogeneity and availability as modulators of such relationship is poorly known.

Methods

We conducted a factorial experiment in microcosms containing grasses, legumes and non-legume forbs communities differing in composition to evaluate how soil heterogeneity and availability (50 and 100 mg N) affect the links between traits and ecosystem functioning. Community-aggregated specific leaf area (SLA_agg) and specific root length (SRL_agg) were measured as both relevant response traits to soil heterogeneity and availability, and significant effect traits affecting ecosystem functioning (i.e., belowground biomass, β-glucosidase and acid phosphatase activities, and in situ N availability rate).

Results

SRL_agg was negatively and significantly associated to β-glucosidase, phosphatase and N availability rate in the high nutrient availability and heterogeneous distribution scenario. We found a significant negative relationship between SLA_agg and availability rate of mineral-N under low nutrient availability conditions.

Conclusions

Soil heterogeneity modulated the effects of both traits and nutrient availability on ecosystem functioning. Specific root length was the key trait associated with soil nutrient cycling and belowground biomass in contrasted heterogeneous soil conditions. The inclusion of soil heterogeneity into the trait-based response-effect framework may help to scale from plant communities to the ecosystem level.     

根状茎型植物扁秆荆三棱对土壤养分异质性尺度和对比度的生长响应

土壤养分的空间异质性在自然界普遍存在, 而克隆植物被认为能很好地适应和利用土壤养分异质性。尽管尺度和对比度是异质性的两个重要属性, 但有关土壤养分异质性的尺度和对比度及其交互作用对克隆植物生长和分株分布格局影响的研究仍比较缺乏。在一个温室实验中, 根状茎型草本克隆植物扁秆荆三棱(Bolboschoenus planiculmis) (异名扁秆藨草(Scirpus planiculumis))被种植在由高养分斑块和低养分斑块组成的异质性环境中。实验为两种尺度处理(大斑块和小斑块)和两种对比度处理(高对比度和低对比度)交叉组成的4种处理组合。在每个处理中, 高养分和低养分斑块的总面积相同; 在所有4种处理中, 土壤养分的总量也完全相同。无论在整个克隆(植株)水平, 还是在斑块水平, 尺度、对比度及其交互作用对扁秆荆三棱的生物量、分株数、根状茎长和块茎数的影响均不显著。然而, 在斑块水平, 扁秆荆三棱在高养分斑块中的生物量、分株数、根状茎长和块茎数均显著高于低养分斑块, 而在高养分斑块中相邻分株间的距离(间隔物长)小于低养分斑块, 并且这种效应均不依赖于斑块尺度的大小和对比度的高低。因此, 在土壤养分异质性环境中, 扁秆荆三棱可以通过缩短间隔物长, 并可能通过提高根状茎的分枝强度, 把较多的分株和潜在分株放置在养分条件好的斑块中。这种响应格局体现出克隆植物的觅食行为, 有利于整个克隆对异质性资源的吸收和利用。然而, 该实验中的尺度和对比度对扁秆荆三棱分株的放置格局均没有显著效应。作者推测, 在一个更大的斑块尺度和(或)对比度范围内, 扁秆荆三棱对土壤养分异质性的响应可能不同。因此, 下一步的研究应涉及更广泛的尺度和对比度。     

Testing experimentally the effect of soil resource mobility on plant competition

Aims The volume of soil beyond a plant's roots from which that plant is able to acquire a particular nutrient depends upon the mobility of that nutrient in the soil. For this reason it has been hypothesized that the strength of competitive interactions between plants vary with soil nutrient mobility. We aimed to provide an experimental test of this hypothesis.Methods We devised two experimental systems to investigate specifically the effect of nutrient transport rates upon intraspecific competition. In the first, the exchange of rhizosphere water and dissolved nutrients between two connected pots, each containing one plant, was manipulated by alternately raising and lowering the pots. In the second experiment, the roots systems of two competing plants were separated by partitions of differing porosity, thereby varying the plants' access to water and nutrients in the other plant′s rhizosphere. In this second experiment, we also applied varying amounts of nutrients to test whether higher nutrient input would reduce competition when competition for light is avoided, and applied different water levels to affect nutrient concentrations without changing nutrient supply.Important findings In both experiments, lower mobility reduced competitive effects on plant biomass and on relative growth rate (RGR), as hypothesized. In the second experiment, however, competition was more intense under high nutrient input, suggesting that low nutrient supply rates reduced the strength of the superior competitor. Competitive effects on RGR were only evident under the low water level, suggesting that under lower nutrient concentrations, competitive effects might be less pronounced. Taken together, our results provide the first direct experimental evidence that a reduction in nutrient mobility can reduce the intensity of competition between plants.     

Root length dynamics in agroforestry with Gliricidia sepium as compared to sole cropping in the semi-deciduous rainforest zone of West Africa

Tree root systems may improve soil fertility through carbon inputs, uptake of leachable nutrients and maintenance of soil biomass, but can at the same time reduce crop yields by competition for water and nutrients. Quantitative information about the positive and negative effects of tree roots and their changes in space and time are necessary for the optimization of agroforestry associations. An alley cropping experiment was layed out as a randomized complete block design on a Plinthic Lixisol/Ferralic Cambisol with Gliricidia sepium hedgerows at 5 m distance, including a sole cropping control. The development of root systems was monitored by sequential soil coring (eight samplings) during one year, with maize and groundnut as crops. Additional information is presented from a single sampling for rice during the foregoing year. Pronounced fluctuations of live root length density indicated an important variability in the nutrient and water uptake capacity of the vegetation. At low total root length density, the hedgerows affected the root development in the agroforestry plots directly by the presence of their root systems. At high root length density, they affected root development mainly by improving crop root growth and influencing the composition of the spontaneous vegetation. The root length density of the hedgerows was too low to compete with the crops for soil resources. The hedgerows tended to increase root length densities in the subsoil when few roots were present, thus possibly reducing the risk of nutrient leaching. However, the length density of the perennial root systems decreased during the cropping season, presumably as an effect of repeated pruning, and attained minimum values almost at the same time as the crops. Trees with denser root systems which are less frequently pruned may be more efficient in achieving closer nutrient cycles, though at the cost of higher root competition with crops.