农林系统研究进展

综述了国内外农林系统的研究进展 ,介绍了农林系统的概念、产生背景和过程及主要的研究方向。从农林系统的结构和分类、农林系统小气候及系统效益评价等 3个方面对当前农林系统的研究现状进行了评述。重点从水分、温度、辐射、光照及人体舒适度等方面分析了农林系统小气候的研究状况 ;从化感作用和地下部分相互作用两个方面介绍了系统组分间的相互作用关系。同时指出农林系统类型较为单一、理论研究落后于实践、基础理论研究相对薄弱等研究中存在的问题。提出农林系统的研究应进一步加强多学科深层次、实质性的交流与合作 ,注重科研机构与生产基层的有机联系 ,加强理论基础研究 ,因地制宜地发展农林系统 ,更好地为生产实践服务。     

海岸带不同复合农林业系统的小气候特征

对海岸带银杏（Ginkgo biloba Linn.)－农作物在种复合经营模式（A.4年生叶用银杏＋农作物;B.6年生果用银杏＋4年生叶用银杏＋农作物;C.6年生材用银杏＋农作物）进行了小气候的同步测定和因子分析。结果表明：太阳辐射的吸收率、空气相对湿度、防风效应都随模式内植被的立体空间层次增加而增加,而气温、地温的日较差和水面蒸发量却随之降低。各模式中影响小气候的主导因子主要是植被结构层次和地表温度,其因子负荷量分别为－0.971和0.9997。三种模式中,果用银杏－叶用银可－农作物复合模式具有更适宜而又稳定的小气候特征。     

黄淮海平原豫北地区农林业系统的能量研究

对黄淮海平原豫北地区农林业系统３种群落类型（沙兰杨－小麦·玉米（ＰＯＴＺ）、泡桐－小麦·玉米（ＰＡＴＺ）和苹果－小麦·花生（ＭＴＡ））进行了研究,结果表明,ＰＯＴＺ类型的年群落净固定能量为４３．６２３５×１０１０Ｊ·ｈａ－１,ＰＡＴＺ为４５．６４２６×１０１０Ｊ·ｈａ－１,ＭＴＡ为４９．６０００×１０１０Ｊ·ｈａ－１．年群落现存能量分别为５５．２１７４×１０１０,５７．７５９５×１０１０和７８．４６９９×１０１０Ｊ·ｈａ－１;群落的光能利用率分别为１．０００,１．０４７和１．１３８％．群落的能量效率分别比传统的农田系统增加１１．８３、１４．４５和２８．２５％．在农业林业系统中,苹果－小麦·花生群落类型为最佳群落类型．     

湘北丘陵林-稻系统镉的迁移

为了研究中南丘陵区林-稻系统镉的迁移规律,2012年5月下旬至9月上旬(中稻稻季)在湘北汩罗市桃林林场选择两种类型的林-稻复合生态系统针对降水、地表径流、山塘水、稻田水及其中镉含量用收支平衡法进行了原位动态研究。结果表明,(1)以降水形式从区域外输入的镉是湘北地域地表系统主要的外来镉源,镉的输入主要集中在稻季的早期;(2)镉以雨水形式输入丘陵林-稻系统后,53%被林地截留,7.5%累积于山塘,11.6%存留于稻田,其余28.9%以稻田水和稻草、谷粒的形式输出林-稻系统;(3)不同林-稻系统比较,混-稻系统对外源镉的固持功能最强,松-稻系统其次,对照系统最弱,其原因在于各系统间岗地森林郁闭度存在差异,郁闭度大能增强岗地对镉的固持能力;(4)在岗地截留镉能力较弱的情况下,山塘能够减缓系统镉的迁移强度;(5)岗地输入山塘水中的大分子有机物能加强镉在稻田中累积。综上所述,林-稻系统镉的累积与雨水常年输入镉有关,系统内岗地森林郁闭度、与有机物输出相关的森林类型影响镉在系统中的迁移和分配。     

农林复合生态系统防护林斑块边缘效应对节肢动物的影响

于2008和2009年在黄淮海平原典型地区商丘民权林场(34°31'-34°52'N, 115°00'-115°28'E)进行。选择杨树林、槐树林和杨槐混交林3种人工林模式,调查节肢动物群落构成、生物多样性及边缘效应对节肢动物群落结构的影响。结果显示,节肢动物科级水平上不同年份间的类群数和个体数差异都不显著(P>0.05),防护林不同模式间个体数(df=2, F=59.48, P<0.001)和类群数(df=2, F=15.44, P<0.001)差异均显著。3种防护林中以杨树林物种丰富度指数较高,S_杨树林(9.65)>S_{杨槐混交林}(8.78)>S_槐树林(7.47);生物多样性指数H'_杨树林(1.78)>H'_{杨槐混交林}(1.65)>H'_槐树林(1.46),其中杨树与槐树林的S和H'差异显著(P<0.05)。杨树林和槐树林边缘效应对节肢动物群落的影响大于杨槐混交林,林地边缘节肢动物的类群数和个体数均较高。节肢动物类群组成表现为林地边缘的偶见种和农田种多于林内。杨树林和槐树林边缘节肢动物多样性指数较高,向林内40m显著下降;而杨槐混交林边缘效应对节肢动物多样性指数的影响较小。综合分析认为,杨树林和槐树林边缘效应对节肢动物群落结构和多样性的影响距离为40m,杨槐混交林距离为20m。单一树种农田防护林斑块不小于80m宽,混交林斑块不小于40m宽,可以保护林内物种生存,维持农田生态系统生物多样性。     

Determining bioclimatic space of Himalayan alder for agroforestry systems in Nepal

Himalayan alder species are proven to be very useful in traditional as well as contemporary agroforestry practice. These nitrogen-fixing trees are also useful in the land restoration. Therefore, understanding the distribution of Himalayan alder and the potential zone for plantation is meaningful in the agroforestry sector. Suitable climatic zones of Alnus spp. were modelled in MaxEnt software using a subset of least correlated bioclimatic variables for current conditions (1950-2000), topographic variables (DEM derived) and Landuse Landcover (LULC) data. We generated several models and selected the best model against random models using ANOVA and t-test. The environmental variables that best explained the current distribution of the species were identified and used to project into the future. For future projections, ensemble scenarios of climate change projection derived from the results of 19 Earth System Models (ESM) were used. Our model revealed that the most favorable conditions for Alnus nepalensis are in central Nepal in the moist north-west facing slope, whereas for Alnus nitida they are in western Nepal. The major climatic factor that contributes to Alnus species distribution in Nepal appears to be precipitation during the warmest quarter for A. nepalensis and precipitation during the driest quarter for A. nitida. Future projections revealed changes in the probability distribution of these species, as well as where they need conservation and where they can be planted. Also, our model predicts that the distribution of Alnus spp. in hilly regions will remain unchanged, and therefore may represent sites that can be used to revitalize traditional agroforestry systems and extract source material for land restoration.     

Water acquisition,sharing and redistribution by roots: applications to agroforestry systems

Plant and Soil - In the face of problems caused by ‘intensive agriculture’ dominated by large areas of monocultures, mixed intercropping mimicking natural ecosystems has been reported...     

Endocytosis in plants: fact or artefact?

Whilst plant cells are apparently equipped with all the necessary molecular machinery for receptor-mediated endocytosis, the physiological role of this process in these cells remains an enigma. In this article, we consider current opinions of endocytosis in plants and define some of the problems that have impeded progress in our under-standing of the part played by endocytosis in the vesicle trafficking pathway.     

Glutathione-mediated detoxification systems in plants

Recent work has highlighted the presence of diverse glutathione-dependent enzymes in plants with potential roles in the detoxification of both xenobiotic and endogenous compounds. In particular, studies on glutathione transferases are further characterising their role in xenobiotic metabolism, and also raising intriguing possible roles in endogenous metabolism. The solution of their three-dimensional structures together with studies on their molecular diversity and substrate specificity is providing new insights into the function and classification of these enigmatic enzymes.     

Alarm systems in higher plants

The defenses of higher plants against a variety of biotic and abiotic stress agents can be grouped into two categories: Preformed and Induced. Induced defensive responses by the plant, or “alarms”—the subject of the present review—can be localized or systemic. Certain alarms, especially those which are induced by necrotizing pathogens, are protective against a wide variety of biotic stress agents. Other responses appear protective but the degree of host plant involvement is unclear. Finally, there are a few induced plant responses which, although protective, do not easily fit our criteria of an “alarm.” Oligosaccharins may be involved as signals in both anti-herbivore and anti-pathogen alarm systems. Other specific components of plant alarms appear to be induced by only one type of stress agent. The specificity of protection, mechanisms of various alarms and comparisons between them are presented.     

Hydraulic conductivities of competing root systems of Grevillea robustaand maize in agroforestry

Models of water uptake in mixed stands of vegetation commonly assume that water is partitioned among competing root systems in proportion to relative root length densities. Such an approach assumes implicitly that roots of different species have equivalent hydraulic properties. This was tested for root systems of Grevillea robustaA. Cunn. and maize (Zea maysL.) at a semi-arid site in Kenya. The hydraulic conductances for roots of both species were measured in situat the scale of the whole root or root system using a high pressure flow meter (HPFM). Hydraulic conductivities (_r) were expressed per unit root length. Root lengths were estimated for maize plants by soil coring and for G. robustausing a fractal branching model calibrated against soil coring. Mean _r was 1.88×10^–7 ±0.28×10^–7kg s^–1 MPa^–1 m^–1 for G. robustaand 1.25×10^–7 ±0.13×10^–7kg s^–1 MPa^–1 m^–1 for maize. Values of _r were not significantly different (P<0.05), suggesting that the assumption of hydraulic equivalence for root systems of the two species may be valid, at least when hydrostatic gradients are the major driving force for water uptake. Differences in conductivities between these species could arise, however, because of variation in the hydraulic properties of roots not accounted for here, for example because of root age, phenology or responses to the soil environment.     

Self-incompatibility systems: barriers to self-fertilization in flowering plants

Flowering plants (angiosperms) are the most prevalent and evolutionarily advanced group of plants. Success of these plants is owed to several unique evolutionary adaptations that aid in reproduction: the flower, the closed carpel, double fertilization, and the ultimate products of fertilization, seeds enclosed in the fruit. Angiosperms exhibit a vast array of reproductive strategies, including both asexual and sexual, the latter of which includes both self-fertilization and cross-fertilization. Asexual reproduction and self-fertilization are important reproductive strategies in a variety of situations, such as when mates are scarce or when the environment remains relatively stable. However, reproductive strategies promoting cross-fertilization are critical to angiosperm success, since they contribute to the creation of genetically diverse populations, which increase the probability that at least one individual in a population will survive given changing environmental conditions. The evolution of several physical and genetic barriers to self-fertilization or fertilization among closely related individuals is thus widespread in angiosperms. A major genetic barrier to self-fertilization is self-incompatibility (SI), which allows female reproductive cells to discriminate between "self" and "non-self" pollen, and specifically reject self pollen. Evidence for the importance of SI in angiosperm evolution lies in the highly diverse set of mechanisms used by various angiosperm families for recognition of self pollen tube development and preventing self-fertilization.     

Improvement of thermal comfort indices in agroforestry systems in the southern Brazilian Amazon

Agroforestry systems can minimize heat stress and improve cattle welfare, but the influence of the forest component in microclimatic changes in the southern Amazon remains unclear. This study aimed to compare the thermal comfort indices in grass monoculture and integrated systems. The three systems were pasture under full sunlight (PFS), integrated (triple-row) livestock-forestry (ILF_T), and integrated (single-row) livestock-forestry (ILFs), across four seasons, for two years, from June 2017 to June 2019. We assessed photosynthetically active radiation (PAR), air temperature, relative humidity, black globe temperature, and wind speed. Thermal comfort indices such as temperature-humidity index (THI), black globe temperature-humidity index (BGHI), and radiant thermal load (RTL) were calculated based on microclimate data daily-collected from 8:00 to 16:00. The ILF_T mean THI (76.8) was slightly lower than ILF_S and PFS. The BGHI and RTL values decreased as shading increased (PFS > ILFs > ILF_T). The most challenging heat stress conditions for grazing animals occurred predominately during winter and autumn. In conclusion, the presence of trees in pastures of the southern Amazon improved the microclimate and, consequently, the thermal comfort indices. Agroforestry systems can foster an environment with a more suitable thermal comfort or less restrictive to animal performance, which contribute to mitigating global climate change for forage-livestock systems in Brazilian Amazon.     

Touch sensitivity in plants: be aware or beware

A recent paper shows that touch sensing and gravity sensing interact to guide roots around obstacles. Upon encountering an object, the touch stimulus induces curvature behind the root tip and partially suppresses the gravity response, enabling the root to navigate around the obstacle while maintaining contact with it. These findings raise questions regarding the nature of touch sensing in roots, the location of the sensors, and the manner in which these sensory systems interact to accomplish obstacle avoidance.     

The role of habitat patches on mammalian diversity in cork oak agroforestry systems

Habitat patches, depending on the degree of differentiation from the matrix, can add few or many elements to the species pool of a particular landscape. Their importance to biodiversity is particularly relevant in areas with complex landscapes, where natural, naturalized, or managed habitats are interspersed by small patches of habitat types with very different biophysical characteristics; e.g., fruit orchards and riparian areas. This is the case of the montado landscape, a cork oak agroforestry system that largely covers south-western Portugal. We evaluated whether the high mammalian biodiversity found in this system is, in part, the cumulative result of the species found in the non-matrix habitats. Our results indicate that in areas where there are inclusions of orchards/olive yards and riparian vegetation in the cork oak woodland, a significantly higher number of mammalian species are present. We further detected a positive effect of low human disturbance on mammal diversity. Ultimately, our results can be used by managers to augment their management options, since we show that the inclusion and maintenance of non-matrix habitat patches in cork oak agro-silvo-forestry systems can help to maximize mammal biodiversity without compromising services associated with agriculture and forestry.     

Indicating soil quality in cacao-based agroforestry systems and old-growth forests: The potential of soil macrofauna assemblage

Soil quality or health is a fuzzy concept that has been vigorously criticized due to the extreme variability of soil and the difficulty of linking soil indicators to soil functions and sustainability. In most soil quality studies some obvious factors or typologies are used as a basis to select the “best indicators” of soil quality, i.e. those that best explain the differences among the plots under study. This is not the case for a variety of natural or agro-ecosystems including the Talamanca cacao-based agroforestry systems (AFS), which present neither a pre-established typology nor a clear framework to evaluate their soil quality. This situation required a selection of indicators based on the literature that was oriented by the non-equilibrium thermodynamic theory. A framework was elaborated through full and minimum indicator sets of baseline soil physical and chemical indicators, along with macrofauna groups. A minimum set of four well-accepted abiotic soil quality indicators (bulk density, sum of bases, pH and carbon) was able to separate cacao AFS plots and forests into five distinct clusters along a low-to-high “soil quality” gradient. The AFS rated as “good” soil quality did not differ from the forest. Abundances of selected macrofauna groups were well correlated with these indicators and helped elucidate the soil quality clusters identified. In particular, high predator abundance indicated proper energy flow and confirmed the high abiotic soil quality, thus confirming the potential of macrofauna groups as apt soil quality indicators. However, these indicators need to be tailored to local conditions. Consequentially, cacao-based AFS in Talamanca are able to conserve soil and provide a high level of soil-related ecological services. Considering the soil an open system where the non-equilibrium thermodynamic theory applies successfully guided indicator selection and could help to reformulate the soil quality definition.     

Indole-metabolizing enzyme systems in tropical plants

Extracts from the leaves of 60 plants from 33 families were screened for their ability to metabolize indole. Of these plants, only 11 species were found to cause the rapid disappearance of indole. There is no correlation between the family and indole disappearance. While eight species can degrade indole anaerobically, Tecoma, Mussaenda and Duranta species require oxygen.