Trait–environment relations for dominant grasses in South African mesic grassland support a general leaf economic model

Question: Following the framework of Suding et al. (2003), we examined whether morphological traits (organismal response), tolerance and competitive effect (specific process response) were associated with grass dominance (abundance response) on burning, mowing, fertilization and soil depth gradients in KwaZulu‐Natal (KZN), South Africa. Location: University of KwaZulu‐Natal, Pietermaritzburg, South Africa. Methods: Using several pot experiments involving 29 grass species in total, we determined the vegetative traits, competitive effect and response, and tolerance to shading for grasses common in closed, tufted mesic grassland in KZN. Results: The primary axis of grass–trait variation was most strongly related to a negative correlation (trade‐off) between growth rate and specific leaf area (SLA), with broad‐leaved, rapidly‐growing grasses (high SLA) occupying one extreme and narrow‐leaved, slow‐growing grasses (low SLA) the other extreme of the first principal component. The low SLA, slow‐growth strategy was found to be a relatively general strategy among grasses dominant in undisturbed, high litter grassland, as well as those adapted to moisture‐stressed habitats. In contrast, grasses dominant in highly productive habitats with some form of disturbance, e.g. mowing, had a broad‐leaved, rapid‐growth strategy. Intermediate combinations of the SLA–growth rate trade‐off were common among grasses dominant under other combinations of disturbance and soil resource availability. Conclusions: Distinct patterns of organismal (SLA, growth rate) and specific process (competitive effect and response, as well as tolerance of shading) responses appeared to be associated with grasses dominant on gradients of burning, mowing, fertilization and soil depth. These organismal and specific process responses were similar to those for North American and European grasses dominant under the same environmental influences, suggesting that some general trait–environment patterns exist at an inter‐continental scale. This general trait–environment relationship appears to be driven by functional adaptive selection along the SLA–environment continuum and its unavoidable trade‐off with growth rate.     

Plasticity of Least Tern and Piping Plover nesting behaviors in response to sand temperature

Birds that nest on the ground in open areas, such as Piping Plovers (Charadrius melodus) and Interior Least Terns (Sternula antillarum athalassos), are exposed to high temperatures in thermally stressful environments. As a result, some ground-nesting avian species have adapted behavioral strategies to maintain thermal regulation of eggs and themselves. We assessed the impact of sand temperature on shorebird nesting behaviors by installing video cameras and thermocouples at 52 Least Tern and 55 Piping Plover nests on the Missouri River in North Dakota during the 2014–2015 breeding seasons. Daily duration and frequency of shading behaviors exhibited a nonlinear relationship with temperature; therefore, we used segmented regressions to determine at what threshold temperature (mean temperature = 25.7^⸰C for shading behavior daily frequency and mean temperature = 25.1^⸰C for shading behavior daily duration) shorebird adults exhibited a behavioral response to rising sand temperatures. Daily nest attendance of both species decreased with increasing sand temperatures in our system. Frequency and duration of daily shading behaviors were positively correlated with sand temperatures above the temperature threshold. Piping Plovers exhibited more and longer shading behaviors above and below the temperature thresholds (below: frequency = 10.30 ± 1.69 se, duration = 7.29 min ± 2.35 se; above: frequency = 59.27 ± 6.87 se) compared to Least Terns (below: frequency = −1.37 ± 1.98 se, duration = −0.73 min ± 1.51 se; above: frequency = 31.32 ± 7.29 se). The effects of sand temperature on avian ground-nesting behavior will be critical to understand in order to adapt or develop recovery plans in response to climate change.     

黄山木兰的丛枝菌根定殖状况

在原产地和引种栽培地采集了国家珍稀濒危植物黄山木兰（Magnolia cylindrica）的根样及其根际土壤样品,研究了根中丛枝菌根真菌（AMF）的定殖状况。AMF在两地黄山木兰的根中均有定殖,并形成典型的Paris-type类型丛枝菌根(AM),原产地黄山木兰的AMF定殖率高于栽培地。用湿筛沉淀法从两地黄山木兰根际土壤中共分离鉴定出5属22种AMF,两地AMF群落相似性系数为0.96。原产地黄山木兰的AMF孢子密度高于栽培地,而Shannon-Wiener多样性指数低于栽培地。研究结果表明,黄山木兰引种栽培后并没有对其根际土壤中AMF的群落结构造成大的改变。     

不同生长光强下8种红树植物幼苗叶片的光响应特征

为探讨红树植物光适应的生理生态策略，对6种真红树植物[无瓣海桑(Sonneratia apetala)、秋茄(Kandelia candel)、木榄(Bruguiera gymnorrhiza)、桐花树(Aegiceras corniculatum)、老鼠簕(Acanthus ilicifolius)、卤蕨(Acrostichum aureum)]和2种半红树植物[银叶树(Heritiera littoralis)、黄槿(Hibiscus tiliaceus)]的1 a生幼苗在不同生长光强(自然光强的100%、45%、30%、10%)下的光合光响应特征进行了研究。结果表明，不同生长光强对红树植物光响应特征的影响因物种而异，遮荫显著提高了秋茄和木榄的最大净光合速率(P_max)，而对其他红树植物的P_max没有显著影响；秋茄在45%光强下具有较高的P_max，木榄的P_max则在45%和30%光强下显著高于其他2个处理。随着生长光强的下降，秋茄幼苗叶片的光饱和点显著上升，木榄、老鼠簕和卤蕨的光补偿点呈下降趋势，木榄和卤蕨的表观量子效率升高的同时暗呼吸速率下降。木榄、老鼠簕和卤蕨具有较强的耐荫性，适宜种植在光强较弱的林下；无瓣海桑、秋茄、桐花树、银叶树和黄槿则适宜作为中上层树种或在郁闭度较低的林下种植。     

遮荫对夏玉米产量及生长发育的影响

在大田条件下研究了不同时期和不同程度遮荫对夏玉米产量及生长发育的影响.结果表明,遮荫显著降低玉米产量.不同时期遮荫对其影响不同,花粒期（从开花到成熟期）遮荫的影响最显著,农大108（ND108）和掖单13号（YD13）遮荫50%、90%处理分别减产67.5%、79.4%和82.9%和86.7%,其次是穗期（从拔节到开花期）遮荫,ND108和YD13分别减产34.1%、55.3%和47.2%、65.7%,而苗期（从出苗到拔节期）遮荫对其影响相对较小,ND108和YD13分别减产16.9%、24.5%和18.9%、24.3%.遮荫对YD13产量的影响大于ND108.遮荫时期对玉米产量的影响显著地大于遮荫程度.遮荫后两个玉米品种的生育进程都延迟,并随着遮荫程度的增加,对其影响加剧.穗期遮荫显著影响玉米的穗分化,花丝数和雄穗分枝数显著降低,对YD13的影响大于ND108.苗期和穗期遮荫显著抑制玉米叶面积、株高和茎节的生长.     

遮光处理对西葫芦幼苗形态特征及光合生理特性的影响

研究了不同遮光处理对西葫芦幼苗形态及光合生理特性的影响.结果表明,在60%透光率条件下,西葫芦幼苗具有较高的相对生长率、净光合速率、气孔导度、蒸腾速率、单叶水分利用效率、饱和蒸汽压、表观量子效率和叶绿素含量,而胞间CO₂浓度较低;西葫芦幼苗具有较高的光饱和点(1 125 μmol·m^-2·s^-1)、较低的光补偿点(15.2 μmol·m^-2·s^-1).弱光下西葫芦幼苗较耐低浓度CO₂,而强光下的幼苗较耐高浓度CO₂.60%透光率下西葫芦幼苗叶片丙二醛和脯氨酸含量最低,而过氧化物酶和过氧化氢酶活性则最高.     

不同光照梯度的遮荫处理对绒毛番龙眼幼苗生长的影响

在不同光照梯度,即100%自然全光照(natural sunlight,NS)、37.3%NS、15.5%NS、4.2%NS、1.6%NS和0.6%NS的人工遮荫条件下,研究了西双版纳季节雨林冠层树种绒毛番龙眼(Pometia tomentosa)幼苗的早期生长和定居后的生长特点。结果表明,光照是影响幼苗生长的重要环境因子。生长早期的幼苗基径和复叶数随遮荫程度的增加而降低;主根长、根冠比、总干重和单株叶面积均以37.3%NS处理最大;比叶面积随遮荫程度的增加而增大,而相对生长率则降低;幼苗株高在0.6%NS下增长最快,表明种子中贮藏的营养物质对幼苗的早期生长可能具有重要作用。37.3%NS处理对定居后绒毛番龙眼幼苗的生长最有利,幼苗的株高、基径、复叶数、叶轴长、复叶最多小叶数、单株叶面积、相对生长率和净同化率均在37.3%NS处理下获得最大增长;幼苗总干重随光照强度的减弱而降低;比叶面积在15.5%NS处理时最大。幼苗比叶面积和根冠比在生长过程中的波动可能是光照和土壤水分共同作用的结果。     

不同生长阶段遮荫对番茄光合作用、干物质分配与叶N、P、K的影响

对番茄植株做了两种不同程度的遮荫处理,观测了夏季午间遮荫对光合速率,干物质积累量及其在根,茎,叶之间的分配,和叶N,P,K的含量以及经济产量的影响,发现不同时期遮荫影响不同。（1）遮荫增加三个阶段（开花早期,盛花期和开花后期）的气孔导度和胞间CO2浓度,显著降低开花早期中午的净化合速率,但盛花期中度遮荫（40%遮荫）使净光合速率随着时间的增加逐渐上升,在开花后期表现更加明显,平均净光合速率比对照高20%以上,蒸腾速率也增加较多。（2）开花早期和盛花期重度遮荫（如本实验中的75%遮荫）显著降低根,茎的干重,而开花后期中度遮荫的根,茎干重高于对照,但遮荫对叶干重的影响不明显。（3）开花早期和盛花期遮荫不明显影响叶片中N,P,K的含量,但开花后期中度遮荫使N,P,K含量增加,（4）开花早期两种遮荫对果实产量影响较小,但盛花期重度遮荫使产量降低,全部产量中无效部分所占的比例上升,开花后期中度遮荫的总产量和有效产量增加,单果重也增加,这些结果表明,在某些时期中度遮荫可以克服夏天辐射过强,气温过高对番茄的不良影响,对番茄生长,干物质积累和提高产量等有利,在生产上有意义。     

遮荫条件下草莓的光合特性变化

对宝交早生和硕丰两个草莓品种遮荫处理后测定其光合特性变化结果表明,遮荫处理使两个草莓品种叶片光合速率显著降低,分别下降了20%和47%,而表观量子效率分别提高了13%和8%.叶片中叶绿素含量升高而可溶性蛋白含量显著降低.光系统Ⅱ电子传递活性(PSⅡ活性)分别下降了22.5%和53.7%.1,5二磷酸核酮糖羧化酶(Rubisco)活性分别降低了19.6%和35.3%.进一步讨论了草莓光饱和速率下降的生理基础.