Silvopastoralism in New Zealand: review of effects of evergreen and deciduous trees on pasture dynamics

Complex interactions between livestock, trees and pasture occur in silvopastoral systems. Between trees and pasture, competition for soil resources (nutrients and water) occurs, becoming especially relevant when one of them is in scarce supply. Trees reduce light and water reaching the understorey layers according to tree density and canopy size. However, they may ameliorate extreme climatological features (reducing wind speed and evapotranspiration, and alleviating extreme temperatures), and improve soil properties, for example, deciduous tree litter may contribute to increased pH and soil nutrient concentrations. During tree establishment, there are generally negligible effects on pasture, irrespective of tree type. However, there is a decline in pasture production and nutritive value under shade with increasing tree age and higher stand density. Under the same conditions, deciduous trees affect pasture later (extinction point of pasture occurs at 85% of canopy closure) than evergreen trees (about 67% for Pinus radiata D. Don). This is mainly because deciduous trees have a leafless period that enables pasture recovery, and their litter smothers pasture less intensely because of its relatively fast decomposition. Silvopastoral studies conducted in New Zealand are reviewed to discuss these effects, and differences in the effects of evergreen and deciduous trees are shown using the examples of P. radiata, and Populus and Salix spp. respectively, which exist in many temperate countries. Future research needs are outlined.     

Pasture production under densely planted young willow and poplar in a silvopastoral system

New Zealand is subject to summer and autumn droughts that limit pasture growth. The planting of willow and poplar trees is one option used to provide green fodder during drought. However, there is a wide concern that such an option can reduce the overall understorey pasture growth. This study evaluated the comparative establishment and growth of densely planted young willow and poplar and their effects on understorey pasture growth. Two experiments were established for 2 years in Palmerston North and Masterton, North Island, New Zealand. In the first experiment, densely planted willow and poplar significantly reduced understorey pasture growth by 24 and 9%, respectively, mainly due to shade, but coupled with soil moisture deficit in summer. In the second experiment, pasture growth in a willow browse block was 52% of that in open pasture as a result of shade and differences in pasture species composition and management. Willow and poplar survival rates were similar (P > 0.05) after 2 years of establishment (100 vs. 90.5%, respectively). However, willow grew faster than poplar in height (1.90 vs. 1.35 m), stem diameter (43.5 vs. 32.6 mm), canopy diameter (69 vs. 34 cm) and number of shoots (8.7 vs. 2.3) at the age of 2 years.     

不同生态环境下水曲柳的解剖结构差异分析

[目的]探究在阴生和阳生2种环境下水曲柳演化出不同内部解剖结构特征。[方法]采用石蜡切片技术、木材离析技术、徒手切片及光学显微摄影技术,分别对阴生和阳生环境下水曲柳(Fraxinus mandschurica Rupr.)叶柄和叶片、木材切面以及木质部导管的结构进行比较研究。[结果]阴生环境下,水曲柳叶柄和叶片的角质层不发达,叶肉细胞通气组织发达,海绵组织不发达,栅栏组织稀疏,导管分子孔径较小,气孔稀疏,表现出植物耐阴性的结构特征。阳生环境下,其叶柄和叶片都表现出切向壁角质层加厚,叶肉细胞小而致密,栅栏组织层数较阴生多,海绵组织致密,可有效折射光强,避免叶片灼伤,维管组织发达,导管孔径较大,运输能力较强,是植物为适应干旱环境所演化出的特有结构。[结论]试验结果为进一步探究植物颉颃逆境及结构植物学的基础研究提供了理论依据,证实了植物内外部形态与环境密切相关。     

黑豆种质苗期耐荫性评价及其根系对弱光胁迫的响应

玉米-大豆复合种植是西南地区重要的生态种植模式之一,而目前耐荫型专用黑豆种质十分匮乏,黑豆的耐荫机理也尚不清楚,这严重影响了该模式的进一步推广。本研究旨在建立黑豆苗期耐荫性评价数学模型,筛选出能够判断黑豆耐荫性的有效指标,并探讨不同耐荫型黑豆根系对弱光胁迫的响应差异,为耐荫型黑豆种质的选育及耐荫机理的阐释奠定基础。试验以23个黑豆种质为研究材料,采用盆栽试验方法,设置自然光和遮荫2个处理。在黑豆植株V3期测定株高、茎粗、下胚轴长度、叶片干重、茎干重、主茎节数、总根长、根表面积、总根体积等形态指标和光合参数、叶绿素荧光参数等生理指标。采用多元统计方法建立黑豆苗期耐荫性评价模型,并根据评价结果,关联分析不同耐荫型黑豆根系对弱光胁迫的响应差异。通过逐步回归分析建立了黑豆苗期耐荫性评价数学模型;并通过该模型,筛选出蒸腾速率、株高、叶干重、最大荧光强度和初始荧光强度等5个鉴定指标。在荫蔽条件下测定苗期黑豆的上述5个指标可实现对黑豆苗期耐荫性的综合评价。同时,对23份黑豆种质的耐荫性综合评价值D进行了聚类分析,结果表明,黑豆种质可划分为耐荫型、中度耐荫型和荫蔽敏感型3类。不同耐荫型黑豆种质的根系结构对弱光胁迫的响应程度不同,黑豆的总根长、根表面积、总根体积、根干重等根系强度指标均表现为耐荫型中度耐荫型荫蔽敏感型。这表明耐荫潜力大的黑豆根系更发达。     

耐弱光基因型马铃薯在遮阴条件下的光合和荧光特性分析

为探寻遮阴对马铃薯光合和荧光特性及吸收光能分配的影响,本研究采用大田试验,以马铃薯不耐弱光品种‘丽薯6号’和耐弱光品种‘中薯20’为材料,出苗后用遮光率70%的黑色遮阳网进行遮阴处理(T),以自然光照为对照(CK),测定了遮阴30 d后马铃薯叶片的光合作用、光响应曲线、CO_2响应曲线、光诱导曲线和叶绿素荧光参数的变化。结果表明:1)遮阴后净光合速率(P_n)、气孔导度(G_s)、蒸腾速率(T_r)、最大净光合速率(P_(max))、光饱和点(LSP)、光补偿点(LCP)较CK显著下降;‘中薯20’的P_n、P_(max)、LSP较高,LCP和暗呼吸速率(R_d)较低。2)不同基因型CO_2响应参数无显著差异,但‘中薯20’的最大羧化速率(V_(cmax))和最大电子传递速率(Jmax)较高,CO_2补偿点(CCP)较低。3)高光诱导过程中,‘中薯20’反应较快,光合能力较强。4)初始荧光(F_o)、最大荧光(F_m)、最大光化学量子效率(F_v/F_m)较CK显著增加,PSⅡ实际光化学量子效率(?F/F_m′)、表观电子传递速率(ETR)和光化学猝灭系数(qP)较CK显著下降,非光化学猝灭系数(NPQ)呈增加趋势。5)非光化学热耗散(ФNPQ)和荧光耗散途径(Фf,d)比例显著增加,光化学猝灭耗散途径(ФPSⅡ)比例显著减少,主要以增加热耗散为主。遮阴后,耐弱光基因型‘中薯20’的NPQ和ФNPQ均高于不耐弱光的‘丽薯6号’,说明‘中薯20’的光合机构保护能力更强。综合分析表明,遮阴后耐弱光基因型马铃薯具有较高的净光合速率、较低的光补偿点、较低的CO_2补偿点、较快的光诱导反应速度和较高的非光化学热耗散能力。     

银杏不同部位叶片叶绿素荧光参数动态变化规律研究

[目的]探讨银杏不同部位叶片叶绿素荧光参数动态变化规律。[方法]以华北地区人工栽培的银杏为试材,研究了其不同部位叶片叶绿素荧光参数的日、季节动态变化规律。[结果]银杏叶片叶绿素荧光参数Fo、Fm、Fv、Fv/Fm、Fm/Fo、Fv/Fo的日变化呈现明显的先减小后增大的动态规律,一般在中午12：00达到最低值,向阳叶片的NPQ在中午时分达到最大值。银杏阴生叶的荧光参数Fm、Fv、Fv/Fm、Fm/Fo、Fv/Fo明显高于阳生叶,但NPQ最高峰出现时刻早于阳生叶,且峰值高于阳生叶,表明银杏阴生叶可能具有更为灵敏的热耗散机制。（3）与阳生叶相比,在不同测定时期阴生叶具有更高的PSⅡ潜在活性和内禀光能转换效率。[结论]为保扩银杏资源提供了理论依据。     

草坪植物耐弱光机理研究进展

在遮荫胁迫下,草坪植物形态特征、解剖结构、光合器官、抗氧化物酶、内源激素以及营养元素的吸收和积累等都会发生一系列变化。本文阐述了草坪植物耐弱光逆境研究的意义、弱光逆境对植物的形态及生理的影响、植物对弱光逆境的生理响应机理和光合调控机制,并对当前草坪植物耐弱光逆境胁迫的研究方向提出自己的看法,旨在为今后的相关研究提供建议。     

不同玉米自交系耐荫性比较

采用人工模拟遮荫的方法,研究了27个玉米自交系耐荫性差异。结果表明,遮荫使所有自交系的叶绿素含量下降,茎粗变细,株高降低,干物质积累下降,生物产量降低。不同自交系对遮荫的反应不同。以综合耐荫系数为指标,对其耐荫性进行了评定,将其分为耐荫性强、耐荫性中等、耐荫性弱3个级别。     

植物遮荫效应的研究进展

植物为了适应遮荫的环境,改变自身的生理生化特性,如叶绿素含量、光合特性、蒸腾特性、气孔导度、与光合作用相关的酶、膜脂过氧化物酶、膜保护酶活性、内源激素含量、游离脯氨酸含量及花色素苷含量等,从而保证植物体自身能在遮荫的条件下充分利用光能进行正常的生命活动.现从遮荫对植物生长环境、生长发育、生理生化特性等方面的影响介绍目前的研究进展.     

不同遮荫方式对生姜生长及产量的影响

不同的遮荫方式与遮荫程度对生姜生长及产量有较大的影响。以覆草（麦秸）的处理植株长势较好，产量最高。其次以遮荫６０％（插姜草）的处理增产效果较好，而不插姜草与过度遮荫则导致产量降低。因覆草省工省力、成本低廉、增产显著，建议在生产上推广应用。