Short‐term harvesting of biomass from conservation grasslands maintains plant diversity

High yields are a priority in managing biomass for renewable energy, but the environmental impacts of various feedstocks and production systems should be equally considered. Mixed‐species, perennial grasslands enrolled in conservation programs are being considered as a source of biomass for renewable energy. Conservation grasslands are crucial in sustaining native biodiversity throughout the US Upper Midwest, and the effects of biomass harvest on biodiversity are largely unknown. We measured the effect of late‐season biomass harvest on plant community composition in conservation grasslands in three regions of Minnesota, USA from 2009 to 2012. Temporal trends in plant species composition within harvested grasslands were compared to unharvested grasslands using mixed effects models. A before‐after control‐impact approach using effect sizes was applied to focus on pre‐ and postharvest conditions. Production‐scale biomass harvest did not affect plant species richness, species or functional group diversity, nor change the relative abundance of the main plant functional groups. Differences in the relative abundances of plant functional groups were observed across locations; and at some locations, changed through time. The proportion of non‐native species remained constant, while the proportion of noxious weeds decreased through time in both harvested and unharvested grasslands at the central location. Ordination revealed patterns in species composition due to location, but not due to harvest treatment. Therefore, habitat and bioenergy characteristics related to grassland plant communities are not expected to change due to short‐term or intermittent late‐season biomass harvest.     

Dry season watering alters the significance of climate factors influencing phenology and growth of saplings of savanna woody species in central Zambia,southern Africa

Although tree growth in southern African savannas is correlated with rainfall in the wet season, some studies have shown that tree growth is controlled more by rainfall in the dry season. If more rainfall occurred in the dry season in future climates, it would affect the growth of savanna trees, especially saplings that have shallower roots which limit access to subsoil water during the dry season when leaf flush and shoot extension occur. Recent paleobotanical evidence has revealed that there was relatively more precipitation in the dry season in eastern Africa in the Eocene than under the current climate. Saplings therefore can be expected to respond more to water addition during the dry season than mature trees that have more stored water and deeper roots that access subsoil water. Accordingly, I hypothesized that irrigation in the dry season should (i) advance the onset of the growing season, (ii) increase growth rates and (iii) alter the growth responses of saplings to climate factors. To test these hypotheses saplings of five savanna woody species were irrigated during the hot‐dry season at a site in central Zambia and their monthly and annual growth rates compared to those of conspecifics growing under control conditions. Although the responses among the species were variable, all irrigated saplings had significantly higher monthly and annual growth rates than control plants. In addition, dry season watering significantly altered the climatic determinants of sapling growth by either strengthening the role of the same climatic factors that were important under control conditions or displacing them altogether. In conclusion, more precipitation during the hot‐dry season is likely to have significant positive effects on sapling growth and consequently reduce the sapling‐tree transition periods and promote future tree population recruitment in some southern African savanna tree species.     

Leaf economics and hydraulic traits are decoupled in five species‐rich tropical‐subtropical forests

Leaf economics and hydraulic traits are critical to leaf photosynthesis, yet it is debated whether these two sets of traits vary in a fully coordinated manner or there is room for independent variation. Here, we tested the relationship between leaf economics traits, including leaf nitrogen concentration and leaf dry mass per area, and leaf hydraulic traits including stomatal density and vein density in five tropical‐subtropical forests. Surprisingly, these two suites of traits were statistically decoupled. This decoupling suggests that independent trait dimensions exist within a leaf, with leaf economics dimension corresponding to light capture and tissue longevity, and the hydraulic dimension to water‐use and leaf temperature maintenance. Clearly, leaf economics and hydraulic traits can vary independently, thus allowing for more possible plant trait combinations. Compared with a single trait dimension, multiple trait dimensions may better enable species adaptations to multifarious niche dimensions, promote diverse plant strategies and facilitate species coexistence.     

The Lusitanian toadfish as bioindicator of estuarine sediment metal burden: The influence of gender and reproductive metabolism

Early diagenetic processes and anthropogenic activities are responsible for metal enrichment in estuarine sediments. The Tagus estuary (Portugal) is no exception, and as a result of past and present pressures, surface sediment contamination is still an issue in some areas. Since such metal loads may be incorporated by benthic organisms, this study analyzed the accumulation of trace metals in the Lusitanian toadfish (Halobatrachus didactylus) in the Tagus estuary. In order to determine the role played by the seasonal reproductive cycle of the Lusitanian toadfish in the bioaccumulation process of trace metals in its tissues, the concentrations of Cd, Co, Cr, Cu, Ni, Pb and Zn were determined in the liver of male and female specimens captured during reproductive and non-reproductive periods. The results showed that metal accumulation in the liver was related simultaneously with gender and season, with females having higher levels of Cd, Cu and Zn during the reproductive period. The metabolic roles of Cu and Zn in embryonic development may explain such results, as both metals accumulated in the female liver to be transported to the gonads later on. Cd, on the other hand, does not have a metabolic role, and the higher concentrations of this metal found in spawning females could be related to the high affinity of Cd to vitellogenin, which is produced in the liver. To assess the species’ potential as an indicator of metal contamination, the concentrations of the seven elements were compared in the muscle tissue of adult, type I males (age ≥5), from two areas with distinct sediment metal loads. Non-essential metals in the muscle reflected the same differences between areas that were found in the sediment samples, evidencing H. didactylus as a potential indicator of those elements bioavailability from the sediment. The results showed that the muscle tissue of adult specimens of a relatively sedentary species such as H. didactylus is a useful indicator of long term accumulation of trace metals. On the contrary, liver concentrations of trace metals showed variation according to the reproductive status, which could lead to overestimate of the environmental status concerning trace metals bioavailability. Spawning season and liver tissue should thus be avoided in biomonitoring studies targeting this benthic fish.     

黄土塬区不同土地利用方式土壤水分消耗与补给变化特征

对黄土塬区不同土地利用方式下2012年3—10月7龄果园(挂果初期)、17龄果园(盛果期)、小麦地、玉米地土壤水文状况进行分析,结果显示,0—600 cm试验土层7龄果园土壤贮水量最高,其次为玉米地、小麦地,17龄果园最低,且不同土地利用方式下贮水量随着降水量的变化而上下波动,但其变化滞后于降水。不同土地利用方式均表现为随土壤深度增加土壤含水量变异程度减弱的特征,且其土壤剖面的水分含量变化存在季节变异。农田和7龄果园中不存在土壤干燥化现象,而17龄果园土壤剖面存在较厚的干燥化土层,其分布深度为320—600 cm。不同的土地利用方式的土壤水分的消耗和补充深度有较大差异,17龄果园消耗深度为500 cm,补充深度为200 cm;7龄果园、玉米地和小麦地消耗深度分别为200、300 cm和300 cm,且补充深度均超过了测定的土壤深度,大于600 cm。     

不同控草措施对高温季节华南地区蔬菜田杂草群落的影响

华南地区高温季节从6月持续到10月,田间杂草危害严重,当前高温季节田间杂草群落发生格局相关的研究资料积累不足。因此在广州高温季节于标准化菜田通过田间杂草调查、小区控草试验和室内土壤培养,研究了杂草群落发生规律和菜田不同清园和土壤处理控草措施对田间杂草群落短期防效和后续影响。结果表明,试验田休耕50 d后,田间杂草群落中禾草类杂草种类较少但发生量明显占优,阔叶类杂草种类较多而危害总体较轻,莎草类杂草种类较少,发生量与阔叶草相当;牛筋草(Eleusine indica)呈现明显的单优势,光头稗(Echinochloa colona)、千金子(Leptochloa chinensis)、碎米莎草(Cyperus iria)、草龙(Ludwigia hyssopifolia)等的盖度也较高。休耕后取田间土壤在不同温度条件下培养的结果亦表明,高温促进禾草类杂草的出苗和幼苗生长(尤其是40℃/35℃)而15℃恒温培养14 d几乎仅有阔叶类杂草出苗。不同控草措施处理的田间试验结果表明,百草枯处理(900 g a.i./hm~2)后阔叶类杂草总盖度上升的趋势被扭转为禾草类杂草持续占优势;喷施百草枯并铲草处理30 d后杂草盖度即恢复至60%以上,而配合喷施丁草胺(1350 ga.i./hm~2)、乙草胺(750 ga.i./hm~2)、精异丙甲草胺(750 ga.i./hm~2)或二甲戊灵(600 ga.i./hm~2)进行土壤处理30 d后可使杂草盖度与仅喷施百草枯处理分别下降72.9%、84.6%、83.9%和77.5%;土壤处理前配合浅翻耕可明显提升控草效果。典范对应分析(CCA)结果表明,控草处理70d后,百草枯、铲草和翻耕处理均对试验田间杂草群落结构具有显著影响(P0.01),田间各主要杂草在CCA排序图中明显分为两个类群:1)光头稗、牛筋草、千金子、马唐(Digitaria sanguinalis)、水虱草(Fimbristylis miliacea)和三头水蜈蚣(Kyllinga triceps);2)草龙、胜红蓟(Ageratum conyzoides)、鳢肠(Eclipta prostrata)、马齿苋(Portulaca oleracea)等阔叶类杂草和碎米莎草。     

水肥互作对滴灌玉米氮素吸收、水氮利用效率及产量的影响

优化水、氮供应是实现作物高产与水肥资源高效利用的有效途径.本文研究了田间试验条件下,水(4500、6750、9000 m³·hm^-2)、氮(0、225、330、435、540 kg·hm^-2)互作对高密度(≥105000 株·hm^-2)滴灌玉米干物质积累、氮素吸收及产量的影响.结果表明: 玉米干物质积累与吸氮量均随灌溉和施氮水平的增加明显升高,当施氮量大于435 kg·hm^-2和灌溉量大于9000 m³·hm^-2时则呈减少趋势.完熟期玉米干物质积累对灌水的响应表现为W₆₇₅₀(36359 kg·hm^-2)>W₉₀₀₀(35077 kg·hm^-2)>W₄₅₀₀(33451 kg·hm^-2),施氮对玉米吸氮量的变化表现为N₄₃₅(459.9 kg·hm^-2)>N₅₄₀(458.1 kg·hm^-2)>N₃₃₀(416.3 kg·hm^-2)>N₂₂₅(351.3 kg·hm^-2),N₄₃₅比N₃₃₀、N₂₂₀分别升高9.1%、32.7%,N₅₄₀比N₄₃₅降低0.6%.在施氮量0～435 kg·hm^-2范围内,玉米最大氮素吸收速率随施氮量增加而升高,在施氮量为435 kg·hm^-2时达最大(6.57 kg·hm^-2·d^-1).灌水与施氮均可显著增加玉米产量、穗粒数和穗粒质量,二者有明显的正交互作用,且以氮为主效应.在施氮0～435 kg·hm^-2范围内,氮肥利用率随施氮量的增加而升高,此后反而降低;灌溉水分生产率随施氮量升高而增加,随灌水量增加而明显下降,灌溉定额为4500～6750 m³·hm^-2时,灌溉水分生产率可达2.57～3.80 kg·m^-3.玉米最高产量18072 kg·hm^-2的施氮量为567.0 kg·hm^-2.最佳经济施氮量为427.9～467.7 kg N·hm^-2时,玉米产量在17109～17138 kg·hm^-2,氮素偏生产力和氮肥利用率分别达122 kg N·hm^-2和45.0%.水氮一体化施肥可实现滴灌玉米高产协同水、氮利用效率的共同提高.     

屋面绿化卷材根系层土壤温度变化特征

根据3种厚度屋面绿化卷材根系层土壤温度、自然条件下的土壤温度和附近气象站大气温度观测资料,采用对比分析、线性回归等方法,对不同屋面绿化卷材根系层土壤温度的变化特征进行了研究。结果表明:屋面绿化卷材根系层土壤温度年变化规律与大气温度年变化规律基本一致;卷材具有一定的隔热保温作用,且随着薄膜厚度的增加,绿化卷材保温隔热效果越明显;不同型号卷材根系层土壤温度的日变幅随薄膜厚度的增加而减小;根系层土温日变幅与厚度关系可拟合成指数函数;不同厚度屋面卷材根系层土壤温度同大气温度之间均存在极显著的线性关系。