黄河三角洲滨海滩涂不同密度柽柳林的根系形态及生长特征

为探讨黄河三角洲滨海滩涂不同密度柽柳根系形态及生长特征,以山东省滨州港附近滨海滩涂的低密度（1100株/hm²）、中密度（4100株/hm²）和高密度（7100株/hm²）柽柳林为研究对象,采用全挖法对不同密度柽柳根系进行挖掘,测定分析柽柳地上生物量、根系生物量、空间分布特征、拓扑结构和连接长度等指标。结果表明：（1）中、高密度下,柽柳对根系生长的投入量更大,以保证对地下资源的吸收利用,根冠比分别为0.59、0.53;而低密度柽柳根冠比为0.44。（2）低、中密度下柽柳根冠生长关系均表现为异速生长,高密度下为等速生长。（3）不同密度柽柳根系生长都以水平分布为主,表现出水平根型特征。中、高密度柽柳根幅及侧根长均小于低密度,低密度柽柳根系水平分布范围最大,可利于增强觅养和固定能力。（4）林分密度与拓扑指数显著相关,低密度柽柳根系拓扑结构趋向于叉状结构（拓扑指数TI=0.62）;中、高密度柽柳拓扑结构趋向于鱼尾形分支（TI=0.86;TI=0.81）。（5）不同密度柽柳根系外部连接长度显著大于内部连接长度,呈现滨海滩涂柽柳根系向外扩张的生长策略。滨海滩涂不同密度柽柳根冠异速生长关系、根系形态及生长特征既有差异性又有相似性,表现出不同的密度适应特征。不同密度柽柳根系均以地表分布、向外扩张为主。低密度柽柳主要通过增加分支,扩大根系生长空间;中、高密度柽柳减少分支,加强对内部资源的利用,以降低与邻株间的竞争。柽柳密度与土壤含水量、电导率、扎根深度、侧根长、拓扑指数显著相关。     

水分和种植密度对干热河谷车桑子生长性状及种内相互关系的影响

水分是干热河谷植物生长过程中最主要的限制因子,种植密度增加也会引起植物生长的资源限制,两者交互作用下植物生长性状及种内关系的变化特征还不清楚。以干热河谷优势植物——车桑子为研究对象,根据元谋干热河谷年均生长季降雨量设置3种水分梯度：高水分、中水分和低水分,同时在各水分梯度下设置4个种植密度：1、2、4、9株/盆,探究水分、种植密度及其交互作用对车桑子生长性状、生物量分配及种内相互作用的影响。结果表明：（1）低水分条件下,车桑子生长和水分生理受到抑制,但车桑子在较低的叶水势下依然能够保持较高的相对含水量;（2）干旱胁迫显著降低了车桑子总生物量和单株生物量,显著增加了枯叶生物量比例,低水分和中水分条件下,增加种植密度对总生物无显著影响;而高水分条件下,增加种植密度显著提高了车桑子总生物量;（3）低水分显著增加了茎、叶生物量的异速生长指数,将更多生物量分配到叶,而种植密度增加显著降低了茎、叶生物量的异速生长指数,增加了茎的生物量分配;（4）通过相对邻体效应的计算,各处理条件下,车桑子种内关系均表现为竞争作用,并且,这种竞争作用的强度随水分的减少和密度的增加而增加。在高密度条件下（9棵/盆）,增加水分不会减轻种内竞争作用。综上,水分和种植密度均会对车桑子个体的生理生长产生影响,在植被恢复过程中,应考虑水分和种植密度对车桑子个体产生的资源限制作用。     

基于容器分区处理探究黑麦草生长对喀斯特不同土壤生境和水分的响应

为了探究不同水分条件下喀斯特地区分布不均、厚薄不一土壤小生境对禾本科草本植物生长的影响,用3种不同深度的容器(对照深度CK,深土D和浅土S)两两组合为6种复合容器(CK-CK、CK-S、CK-D、D-D、S-D和S-S)以实现容器分区,研究了黑麦草的根系生长、生物量积累及其分配特征。结果表明:1)在水分充足(W_0)条件下,组合了浅土容器和深土容器的处理中,黑麦草的根系生长(根长、根直径、根表面积和根生物量)均低于对照容器(CK-CK),且有浅土容器的组合处理(S-S,S-D,CK-S)受抑制程度大于有深土容器的组合处理(CK-D,D-D);当水分含量降低后,即中水(W_1)和低水(W_2)条件下,有深土容器的组合[D-D和(或)CK-D]根系生长与对照相比显著增加,而有浅土容器的组合[S-S和(或)CK-S]根系生长与对照相比显著降低。2)对比同一处理不同容器分区中黑麦草生长指标发现,在水分充足情况下,深土容器和浅土容器均会抑制植物生长,而当水分减少,S区根系生长被严重抑制,但D区根系增长优势明显。3)水分充足条件下,根冠比未受到显著影响;当水分降低时,组合了深土容器的处理根冠比均有升高的趋势,组合了浅土容器的处理根冠比有降低趋势。由此可见,不同土壤生境带来的物理空间限制会影响植物根系生长和生物量积累与分配,但水分的减少会改变根系生长及生物量积累对不同土壤生境的响应:在水分充足时,土壤物理空间是影响根系生长和生物量积累与分配的主要因子,黑麦草主要发展浅层根系。而当水分减少时,黑麦草根系在浅层土壤中无法获取供给生长代谢活动的足量水分,更倾向于将有限的有机物分配给根,通过根系伸长、表面积和体积增大、直径增粗等策略加强水分吸收,从而增强对干旱的抗逆性,提高对土壤和水分异质性的适应。     

川西云杉幼苗非结构性碳水化合物对土壤温度和水分变化的响应

选取5年生川西云杉（Picea balfouriana）幼苗作为试验材料，于生长季模拟土壤温度和水分变化，研究不同土壤温度和水分处理对幼苗各器官生物量和非结构性碳水化合物（NSC）浓度的影响，以期加深对高海拔树木碳水化合物生理的理解，并为全球气候变化下植物的生理生态响应和动态变迁研究提供基础数据。于人工气候室内采用嵌套设计，设置5个土壤温度梯度（2、7、12、17、22℃），每个温度处理下3个土壤水分处理（干旱处理、正常水分含量处理、饱和水分含量处理）。每9株幼苗为同一个处理，共135株幼苗。试验处理4个月后，测定幼苗各器官生物量、可溶性糖、淀粉和NSC浓度。土壤温度对幼苗总生物量无显著影响，但土壤低温显著降低了根生物量和根冠比；干旱和饱和水分胁迫在较高的土壤温度处理下显著降低了根生物量和根冠比。随着土壤温度降低，各器官可溶性糖、淀粉和NSC浓度并未降低，反而呈现出升高或不变的趋势。。在土壤低温处理下（2和7℃）干旱显著降低了当年生叶的淀粉和NSC浓度以及当年生枝的淀粉浓度；在2和7℃时，干旱和饱和水分胁迫显著降低了根中淀粉和NSC浓度。土壤低温和水分胁迫对幼苗地上地下生物量分配影响显著，分配给光合器官的生物量相对增多。土壤低温并没有导致碳受限，甚至各器官NSC浓度随着土壤温度降低有升高的趋势，因此，土壤低温下非结构性碳水化合物的不足不是限制川西云杉幼苗存活和生长的原因，从侧面支持了林线形成的"生长抑制"假说。此外，干旱胁迫在土壤低温下很可能会导致川西云杉的"碳饥饿"。     

福寿螺对稻田水生植物群落实验的影响

福寿螺是在我国南方地区危害水稻生产的一种外来入侵软体动物,已被世界自然保护联盟入侵生物专家组列为100种危害最为严重的外来入侵物种之一。在水域生态系统中福寿螺主要以摄食各种水生植物而生存。以水稻、大薸、水葫芦、粉绿狐尾藻、水花生和鸭舌草构成的稻田水生植物群落为对象,研究了低密度（4 株/m²）、中密度（8 株/m²）和高密度（12 株/m²）福寿螺处理对稻田水生植物群落的影响,同时结合福寿螺的食物选择性实验分析其相关行为特性。结果表明：1）低密度、中密度和高密度福寿螺处理1周内水稻密度均急剧下降,高密度福寿螺造成水稻密度下降超过70%,2周后福寿螺危害水稻秧苗的程度减轻;2）各密度处理福寿螺均抑制了水花生和鸭舌草扩散,第8周时高密度福寿螺处理中水花生和鸭舌草的密度仅为对照的30%和25%。同时,低密度福寿螺处理中的水花生和鸭舌草的密度显著高于中密度和高密度处理。不同密度福寿螺处理对水葫芦、大薸和粉绿狐尾藻影响不明显;3）水稻的日均密度增长率为负值,低密度、中密度和高密度福寿螺处理间存在明显差异,且均显著低于对照。水花生和鸭舌草的日均密度增长率虽为正值,但显著低于对照,水葫芦、大薸和粉绿狐尾藻的日均密度增长率和对照无差异。福寿螺日均密度增长迅速,各密度处理无显著差异。福寿螺对水稻、水花生、鸭舌草的选择性显著高于水葫芦、粉绿狐尾藻和大薸;4） 福寿螺引入8周后稻田水生植物群落物种多样性Simpson指数、Shannon指数和均匀度指数均显著降低。Simpson指数的大小顺序为：对照 > 低密度 > 中密度、高密度,Shannon指数和均匀度指数的大小顺序为：对照 > 低密度 > 中密度>高密度。说明福寿螺对供试水生植物有明显的选择性,其入侵会严重危害稻田水生植物群落的物种多样性。     

风对黄花蒿水力学性状和生长的影响

吹风会影响到植物的水力学结构、光合作用、生物量分配以及植物的力学性状,研究风对植物的综合影响有助于深入了解植物应对风胁迫的响应机制。以黄花蒿为研究对象,每天吹风4h,风速为5m/s,吹风处理60d,测定了风吹条件下黄花蒿的水力学特征、光合作用、生物量分配和茎干力学特性。结果表明:在风吹条件下,黄花蒿正午水势显著低于对照,茎干导水损失率(PLC)增加了16%,最大光合速率仅为对照的62%,气孔导度为对照的55%。在试验结束时风吹植株株高仅为对照的68%,但基茎显著高于对照,同时风吹显著降低了黄花蒿的总生物量,但根冠比显著高于对照,风吹显著减小了茎导管直径和导管密度,风吹植物导管直径和导管密度分别为对照的77%和55%,同时,风吹植物茎干导水率显著低于对照,但茎干的抗弯刚度显著高于对照。以上结果表明风吹抑制了植物的水分输导能力,导致叶片水分匮缺,限制了植物的光合作用。风吹增加了茎干的力学稳定性,但同时降低了茎干的水分输导能力,这是植物茎在力学性状和水分输导之间的权衡。这种改变有利于在有风条件下维持植物的力学稳定性,但同时降低了水分输导能力。     

川西亚高山红桦幼苗土壤蔗糖酶活性对温度和大气二氧化碳浓度升高的响应

研究了不同月份、不同密度下川西亚高山丘桦（Betula　albo—sinensis）幼苗土壤蔗糖酶活性对温度升高（ET）、大气CO2浓度升高（EC）及其复合作用（ETC）的响应．结果表明：ET处理下,各月份土壤蔗糖酶活性均表现出不同程度的提高,其中5、6、9和10月份达到显著水平（P〈0．05）;EC处理下,各月份土壤蔗糖酶活性均显著提高,各月份土壤蔗糖酶活性表现为高密度根际土壤（HR）〉低密度根际土壤（LR）〉高密度非根际土壤（HN）〉低密度非根际土壤（LN）;不同月份的土壤蔗糖酶活性对ETC和遮荫（CS）处理的响应不同,其响应动态与季节变化、植物密度以及蔗糖酶在土壤中的位置密切相关．     

本地和外来草本物种对水分条件时间异质性的可塑响应

极端气候导致的干旱和水淹事件频发，影响了外来植物和本地植物的生长。为了解外来种和本地种植物对干旱和水淹事件发生顺序的响应，探讨草本植物适应水分时间异质性的策略，该文以美国蒙大拿州西部4种本地植物和4种外来植物为研究对象，将所有植物分别进行持续湿润(对照，CK)、水淹-干旱(I-D)和干旱-水淹(D-I)处理，并观测一系列形态和生物量特征的变化。结果表明：(1)与CK相比，D-I和I-D处理均显著降低了外来种的总生物量(P<0.05)。(2)D-I显著降低了本地种早期总生物量、后期地下生物量和根冠比，但显著提高了其后期的相对生长(P<0.05)。(3)D-I处理显著降低了所有植物的地下-地上生物量关系的异速指数，外来种异速指数显著高于本地种(P<0.05)。综上认为，极端事件(水淹和干旱)的发生顺序能改变外来植物和本地植物的生物量分配，早期干旱比后期干旱更容易减少植物生物量的积累，但能促进本地种后期的生长；本地种在环境胁迫下不被降低的总生物量表现说明维持表型稳定的能力较强；D-I处理下本地种和外来种地上和地下生物量关系的分配方式不同。     

不同水分处理对狗牙根种内相互作用的影响

以狗牙根当年生扦插苗为试验材料,根据库区河岸带水分特征设置4种水分处理方式:水分对照组(CK)、水淹与干旱交替组(FD)、土壤水分饱和组(LF)和全淹组(FL),4种密度方式:对照(1株/盆)、低密度(2株/盆)、中密度(4株/盆)及高密度(12株/盆),探究狗牙根生长及形态响应,并验证胁迫梯度假说。结果表明:(1)狗牙根各生物量随水分胁迫强度的增加显著下降(P0.001);密度处理和二者交互作用显著影响狗牙根叶干重、茎干重、根干重、地上生物量和总生物量(P0.001)。(2)水分处理显著影响狗牙根各形态指标(P0.001);密度和二者交互作用显著影响狗牙根分枝数、总茎长和节间长(P0.001)。(3)CK组和LF组狗牙根生物量相对邻体效应(RNE)均为负值,表明其种内关系为竞争关系。FL组各密度组生物量RNE值均为正值,其种内关系转化为促进关系。(4)中高密度组总茎长RNE值随水分胁迫增加而增大。研究表明:(1)狗牙根对不同的水分胁迫均表现出积极响应,可考虑将狗牙根用于库区河岸带植被重建。(2)随种植密度的增大,狗牙根生长及形态均表现出一定的负面效应。(3)本试验在一定程度上支持胁迫梯度假说,但尚需更多概念模型将其改进完善。     

西南喀斯特地区两种草本对干湿交替和N添加的生长响应

喀斯特地区的"岩溶干旱"和频繁的变水环境成为喀斯特地区植被生长和分布的重要选择压力,是该地区植被恢复重建的主要障碍因子。N沉降也会对喀斯特地区的生态系统造成难以预测的影响。为了探究喀斯特地区草本植物对干湿交替和N添加的生长响应,以苍耳(Xanthium sibiricum)和三叶鬼针草(Bidens pilosa)为研究对象,通过盆栽水分受控实验,研究了5种不同水分处理[对照组(CK)、干旱组(D)、1周干湿交替处理组(DW-1)、2周干湿交替处理组(DW-2)和3周干湿交替处理组(DW-3)]与N添加(N+、N-)对两种草本植物生长和生物量的影响。结果表明,干旱胁迫抑制了植物生长和生物量的积累,株高、叶面积、总根长和根体积等生长指标和地上生物量均显著降低,根冠比增大。不同程度的干湿交替对植物的生长和生物量的积累均表现出一定程度的补偿效应,但这种补偿效应的大小随着干旱持续时间的延长而减弱。N添加对植物的生长和生物量积累有显著地促进作用,株高、根表面积、根体积和根生物量较对照组显著增加,但这种促进作用随着干旱历时的增加而减弱,可能与土壤水分状况有关。同时,N添加还影响着植物生物量的分配,在促进两种植物地上和地下生长的同时,还促进了植物根冠比的增加。     

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.     

Effects of competition on root–shoot allocation in <Emphasis Type="Italic">Plantago lanceolata</Emphasis> L.: adaptive plasticity or ontogenetic drift?

We investigated how shoot and root allocation in plants responds to increasing levels of competitive stress at different levels of soil fertility. In addition, we analyzed whether different responses were due to adaptive plasticity or should be attributed to ontogenetic drift. Plantago lanceolata plants were grown during 18 weeks at five plant densities and four nutrient supply levels in pots in the greenhouse. Thereafter root and shoot biomass was measured. There were clear negative effects of increasing plant densities on plant weights revealing strong intraspecific competition. At the lower N-treatments, the proportional allocation to root mass increased with increasing competitive stress, indicating the important role of belowground competition. At the higher N-supply rate, the relationship between competitive stress and shoot to root ratio was neutral. These responses could not be attributed to ontogenetic drift, but could only be explained by assuming adaptive plasticity. It was concluded that at lower N-supplies belowground competition dominates and leads to increased allocation to roots, while at the higher N-supply competition for soil resources and light had balanced impacts on shoot and root allocation. An alternative hypothesis explaining the observed pattern is that light competition has far less pronounced impacts on root–shoot allocation than nutrient deprival.     

Water and nitrogen addition differentially impact plant competition in a native rough fescue grassland

We examined how water and nitrogen addition and water–nitrogen interactions affect root and shoot competition intensity and competition–productivity relationships in a native rough fescue grassland in central Alberta, Canada. Water and nitrogen were added in a factorial design to plots and root exclusion tubes and netting were used to isolate root and shoot competition on two focal species (Artemisia frigida and Chenopodium leptophyllum). Both water and nitrogen were limiting to plant growth, and focal plant survival rates increased with nitrogen but not water addition. Relative allocation to root biomass increased with water addition. Competition was almost entirely belowground, with focal plants larger when released from root but not shoot competition. There were no significant relationships between productivity and root, shoot, or total competition intensity, likely because in this system shoot biomass was too low to cause strong shoot competition and root biomass was above the levels at which root competition saturates. Water addition had few effects on the intensity of root competition suggesting that root competition intensity is invariant along soil moisture gradients. Contrary to general expectation, the strength of root competition increased with nitrogen addition demonstrating that the relationship between root competition intensity and nitrogen is more complex than a simple monotonic decline as nitrogen increases. Finally, there were few interactions between nitrogen and water affecting competition. Together these results indicate that the mechanisms of competition for water and nitrogen likely differ.     

Counteractive biomass allocation responses to drought and damage in the perennial herb Convolvulus demissus

Herbivory and water shortage are key ecological factors affecting plant performance. While plant compensatory responses to herbivory include reallocation of biomass from below‐ground to above‐ground structures, plant responses to reduced soil moisture involve increased biomass allocation to roots and a reduction in the number and size of leaves. In a greenhouse study we evaluated the effects of experimental drought and leaf damage on biomass allocation in Convolvulus demissus (Convolvulaceae), a perennial herb distributed in central Chile, where it experiences summer drought typical of Mediterranean ecosystems and defoliation by leaf beetles and livestock. The number of leaves and internode length were unaffected by the experimental treatments. The rest of plant traits showed interaction of effects. We detected that drought counteracted some plant responses to damage. Thus, only in the control watering environment was it observed that damaged plants produced more stems, even after correcting for main stem length (index of architecture). In the cases of shoot : root ratio, relative shoot biomass and relative root biomass we found that the damage treatment counteracted plant responses to drought. Thus, while undamaged plants under water shortage showed a significant increase in root relative biomass and a significant reduction in both shoot : root ratio and relative shoot biomass, none of these responses to drought was observed in damaged plants. Total plant biomass increased in response to simulated herbivory, apparently due to greater shoot size, and in response to drought, presumably due to greater root size. However, damaged plants under experimental drought had the same total biomass as control plants. Overall, our results showed counteractive biomass allocation responses to drought and damage in C. demissus. Further research must address the fitness consequences under field conditions of the patterns found. This would be of particular importance because both current and expected climatic trends for central Chile indicate increased aridity.     

水稻光合碳在植物-土壤系统中的分配及其对CO2升高和施氮的响应

采用¹³C-CO₂进行连续标记,研究水稻分蘖期和孕穗期光合碳在植株-土壤系统中的分配及其对大气CO₂浓度升高(800 μL·L^-1)和施氮(100 mg·kg^-1)的响应.结果表明: CO₂浓度升高显著提高分蘖期根系生物量和孕穗期地上部生物量,并使生物量根冠比在分蘖期增加,而在孕穗期减小.CO₂浓度升高条件下,施氮使水稻地上部分生物量增加,却显著降低了孕穗期水稻根系生物量.CO₂浓度升高使光合¹³C在孕穗期向土壤的输入显著增加,然而施肥并没有促进由CO₂浓度升高驱动的光合¹³C在土壤中的积累,而且还降低了土壤中的光合¹³C的分配比例.综上,CO₂浓度升高显著提高了稻田土壤光合碳输入,促进稻田有机碳周转;施氮促进了水稻地上部的生长,却降低了光合碳向地下的分配比例.     

Understanding plant rooting patterns in semi‐arid systems: an integrated model analysis of climate,soil type and plant biomass

Aim A consistent set of root characteristics for herbaceous plants growing in water‐limited environments has been developed based on compilations of global root databases, but an overall analysis of why these characteristics occur is still missing. The central question in this study is whether an ecohydrological model which assumes that rooting strategies reflect maximization of transpiration can predict the variations in rooting strategies of plants in dry environments. Location Arid ecosystems across the globe. Methods A model was used to explore interactions between plant biomass, root–shoot allocation, root distribution, rainfall, soil type and water use by plants. Results Model analyses showed that the predicted shifts in rooting depth and root–shoot allocation due to changes in rainfall, soil type and plant biomass were quite similar to observed shifts. The model predicted that soil type, annual rainfall and plant biomass each had strong effects on the rooting strategies that optimize transpiration, but also that these factors have strong interactive effects. The process by which plants compete for water availability (soil evaporation or drainage) especially affected the depth distribution of roots in the soil, whereas the availability of rainfall mainly affected the optimal root–shoot allocation strategy. Main conclusions The empirically observed key patterns in rooting characteristics of herbaceous plant species in arid environments could be explained in this theoretical study by using the concept of hydrological optimality, represented here by the maximization of transpiration.     

水稻光合碳在植物-土壤系统中的分配及其对CO2升高和施氮的响应

采用¹³C-CO₂进行连续标记,研究水稻分蘖期和孕穗期光合碳在植株-土壤系统中的分配及其对大气CO₂浓度升高(800 μL·L^-1)和施氮(100 mg·kg^-1)的响应.结果表明: CO₂浓度升高显著提高分蘖期根系生物量和孕穗期地上部生物量,并使生物量根冠比在分蘖期增加,而在孕穗期减小.CO₂浓度升高条件下,施氮使水稻地上部分生物量增加,却显著降低了孕穗期水稻根系生物量.CO₂浓度升高使光合¹³C在孕穗期向土壤的输入显著增加,然而施肥并没有促进由CO₂浓度升高驱动的光合¹³C在土壤中的积累,而且还降低了土壤中的光合¹³C的分配比例.综上,CO₂浓度升高显著提高了稻田土壤光合碳输入,促进稻田有机碳周转;施氮促进了水稻地上部的生长,却降低了光合碳向地下的分配比例.     

Phenotypic plasticity of <Emphasis Type="Italic">Chenopodium murale</Emphasis> across contrasting habitat conditions in peri-urban areas in Indian dry tropics: Is it indicative of its invasiveness?

Phenotypic plasticity is an important plant trait associated with invasiveness of alien plants that reflects its ability to occupy a wide range of environments. We investigated the phenotypic response of Chenopodium murale to resource variability and ontogeny. Its plant-level and leaf-level traits were studied at high-resource (HR) and low-resource (LR) sites in peri-urban areas in Indian dry tropics. Plants at LR had significantly higher root length, root/shoot biomass ratio, stem mass and root mass fractions. Plants at HR had higher shoot length, basal diameter, leaf mass fraction and leaf area ratio. Leaf-level traits like leaf area and chlorophyll a were also higher here. Mean plasticity indices for plant- and leaf-level traits were higher at HR. With increasing total plant biomass, there was significant increase in the biomass of leaf, stem, root, and reproductive parts, and root and shoot lengths, whereas root/shoot length ratio, their biomass ratio, and leaf and root mass fractions declined significantly. Allocation to roots and leaves significantly decreased with increasing plant size at both sites. But, at any size, allocation to roots was greater at LR, indicative of optimization of capture of soil nutrients, whereas leaf allocation was higher at HR. Consistently increasing stem allocation equaled leaf allocation at comparatively higher shoot lengths at HR. Reproductive biomass comprised 10–12% of the plant’s total biomass. In conclusion, the success of alien weed C. murale across environmentally diverse habitat conditions in Indian dry tropics can be attributed to its high phenotypic plasticity, resource utilization capability in low-resource habitats and higher reproductive potential. These characteristics suggest that it will continue to be an aggressive invader.     

Periodic carbon flushing to roots of Quercus rubra saplings affects soil respiration and rhizosphere microbial biomass

Patterns of root/shoot carbon allocation within plants have been studied at length. The extent, however, to which patterns of carbon allocation from shoots to roots affect the timing and quantity of organic carbon release from roots to soil is not known. We employed a novel approach to study how natural short-term variation in the allocation of carbon to roots may affect rhizosphere soil biology. Taking advantage of the semi-determinate phenology of young northern red oak (Quercus rubra L.), we examined how pulsed delivery of carbon from shoots to roots affected dynamics of soil respiration as well as microbial biomass and net nitrogen mineralization in the rhizosphere. Young Q. rubra exhibit (1) clear switches in the amount of carbon allocated below-ground that are non-destructively detected simply by observing pulsed shoot growth above-ground, and (2) multiple switches in internal carbon allocation during a single growing season, ensuring our ability to detect short-term effects of plant carbon allocation on rhizosphere biology separate from longer-term seasonal effects. In both potted oaks and oaks rooted in soil, soil respiration varied inversely with shoot flush stage through several oak shoot flushes. In addition, upon destructive harvest of potted oaks, microbial biomass in the rhizosphere of saplings with actively flushing shoots was lower than microbial biomass in the rhizosphere of saplings with shoots that were not flushing. Given that plants have evolved with their roots in contact with soil microbes, known species-specific carbon allocation patterns within plants may provide insight into interactions among roots, symbionts, and free-living microbes in the dynamic soil arena.     

Above-ground competition does not alter biomass allocated to roots in Abutilon theophrasti

We tested whether plants allocate proportionately less biomass to roots in response to above-ground competition as predicted by optimal partitioning theory. Two population densities of Abutilon theophrasti were achieved by planting one individual per pot and varying spacing among pots so that plants in the two densities experienced the same soil volume but different degrees of canopy overlap. Density did not affect root:shoot ratio, the partitioning of biomass between fine roots and storage roots, fine root length, or root specific length. Plants growing in high density exhibited typical above-ground responses to neighbours, having higher ratios of stem to leaf biomass and greater leaf specific area than those growing in low density. Total root biomass and shoot biomass were highly correlated. However, storage root biomass was more strongly correlated with shoot biomass than was fine-root biomass. Fine-root length was correlated with above-ground biomass only for the small subcanopy plants in crowded populations. Because leaf surface area increased with biomass, the ratio between absorptive root surface area and transpirational leaf surface area declined with plant size, a relationship that could make larger plants more susceptible to drought. We conclude that A. theophrasti does not reallocate biomass from roots to shoots in response to above-ground competition even though much root biomass is apparently involved in storage and not in resource acquisition.