农田向农林复合系统转变过程中土壤物理性质的变化

以渭北黄土区农林实践中被广泛采用的核桃-小麦间作复合模式为研究对象,以两物种的单作系统为对照,研究单作农田向农林复合系统转变对土壤物理性质的影响,为农林复合系统经营管理和模型的建立提供理论依据.结果表明: 核桃-小麦间作对土壤物理性质的改善作用主要发生在0～40 cm土层.核桃-小麦间作可以避免表层(0～20 cm)土壤容重升高,同时在20～40 cm土层对单作农田形成的犁底层也有显著的改善作用.核桃-小麦间作对各土层田间持水量均表现出持续的改善作用,除在20～40 cm土层略低于核桃单作外,其他从第5年开始均高于两单作系统.核桃-小麦间作对各土层土壤孔隙度均存在持续的改善作用,在0～20 和20～40 cm土层与两单作系统相比存在显著差异,同时也能提高毛管空隙度的比例.农田向农林复合系统转变过程中对土壤容重、田间持水量、土壤孔隙度均有持续的改善作用,且对浅层土壤的改善作用强于深层土壤.     

不同磷水平下小麦-蚕豆间作根系形态的变化及其与内源激素的关系

采用水培方法,研究了不同磷水平下小麦-蚕豆间作体系根系形态变化及其与内源激素的相关关系。结果表明: 与单作小麦相比,在低磷(1/2P)水平下,小麦-蚕豆间作能显著增加小麦的根长,显著减少小麦根系的平均直径,显著增加根系的表面积;在常规磷(P)水平下,间作能显著降低小麦根系的平均直径,有增加小麦根长和根表面积的趋势;与单作蚕豆相比,间作能明显促进蚕豆根系的增长,同时增加蚕豆根表面积。在1/2P水平下,间作能显著提高小麦和蚕豆根系中的生长素(IAA)、脱落酸(ABA)、水杨酸(SA)和茉莉酸(JA)含量;在P水平下,间作能显著提高小麦根系中的IAA、ABA和JA含量,单、间作小麦根系中的SA含量没有显著差异,间作显著增加了蚕豆根系中ABA和SA含量,单、间作蚕豆根系中的IAA和JA含量无显著差异。单作条件下,小麦和蚕豆根系中的内源激素(IAA、ABA、SA和JA)含量与其根系形态(根长、根平均直径和根表面积)无显著相关性;间作条件下,小麦和蚕豆根系中的IAA含量与根长和根表面积之间存在明显的正相关关系。由此可见,小麦-蚕豆间作能够诱导小麦和蚕豆根系IAA的增加。这种变化可能是驱动间作系统根系形态变化的重要因子。     

基于稳定碳同位素技术的华北低丘山区核桃-小麦复合系统种间水分利用研究

农林复合系统的林木和作物会充分利用水肥光热等资源、而在资源亏缺时也可能产生竞争,在华北低丘山区等水资源紧缺地区,种间水分竞争尤为突出。在冬小麦返青期、拔节期、灌浆期和成熟期4个生育期,测算了该地区核桃-小麦间作系统和单作小麦不同组分的稳定碳同位素组成(Stable carbon isotope ratio,δ13C)和核桃树干液流,结合生物量和气象数据资料计算出水分利用效率(water use efficiency,WUE)和耗水量(Water use,WU)。结果表明,间作核桃树、间作小麦和单作小麦的WUE分别为10.771—21.233、9.946—19.149和9.878—18.431 mmol C/mol H2O。单作小麦WUE在拔节期显著小于间作小麦。间作系统总耗水量为1755.19 t/hm2,比单作系统的2538.13 t/hm2少30.85%。核桃-小麦间作系统中,核桃耗水量占系统总耗水量的36.34%,在小麦的生长前期所占比例最多、在小麦旺盛生长期所占比重较小,而小麦越往生长后期需水越多。核桃与间作小麦的需水期错开,在时间上避免水分竞争。距离核桃树越近浅层土土壤含水量越高、而深层土越低,表明核桃主要吸收深层水,而间作小麦主要吸收浅层水,从位置上避免水分竞争。单作小麦产量、总生物量和总耗水量分别比核桃间作小麦的高26.79%、27.12%、36.30%(P=0.001、P=0.033、P=0.050)。间作核桃和单作核桃的单株果实产量平均分别为0.88和0.94 kg(P=0.829)。然而,核桃-小麦间作系统的产量土地当量比(Land equivalent ratio,LER)和产值水分利用效率(WUE ofeconomics,WUEe)却分别达到1.67和25.92元.mm-.1hm-2,比单作系统明显提高、水资源获得高效利用,同时具备生产优势和经济优势。     

核桃-大豆间作系统细根分布及地下竞争

以晋西黄土区核桃-大豆间作系统为研究对象,采用分层挖掘法对核桃-大豆间作系统细根分布特征及地下竞争状况进行研究,旨在为该地区果农间作系统的高效可持续经营提供科学依据。结果表明:核桃细根在垂直方向上主要分布在0～40cm土层内,水平方向上55.7%的细根集中分布在距树行0.5～1.5m区域中;间作物大豆的根系在垂直方向上集中分布在0～20cm土层内,水平方向上根干重随距树行距离的增加呈增加趋势;在水平方向上距树行1.0～2.5m的区域是核桃和大豆地下种间竞争主要发生区,其中以1.5～2.0m区域的竞争最为剧烈。     

华北石质山区核桃-绿豆复合系统氘同位素变化及其水分利用

通过对比核桃枝条和绿豆茎内δD值差异来分析核桃和绿豆水分来源和利用。结果表明,核桃-绿豆农林复合系统的根系在表层土壤(0—30cm)中交叉存在,生态位重叠。旱季中表层土壤含水量与δD值之间存在显著的负相关关系(R2=0.77,P=0.02),雨季相关关系不显著(R2=0.03,P=0.73)。δD值分析表明,旱季中核桃利用深层土壤(30—80cm)水分占总水分来源的51%以上,雨季中则主要利用浅层土壤水分,间作绿豆和单作绿豆主要利用表层土壤水分。雨季中表层土壤水分能同时满足核桃和绿豆生长需要,但复合系统中光能竞争导致间作绿豆光合速率显著地低于单作绿豆。旱季间作绿豆0—20cm土壤水分含量、凌晨叶片水势和光合速率明显高于单作绿豆,显示间作绿豆体内水分状况好于单作绿豆。线性模型分析结果显示间作绿豆体内约有1.58%—5.39%的水分来核桃夜晚水力提升,表明复合系统在旱季一定程度上缓冲季节性水分胁迫对农作物生长的影响。     

油茶-鼠茅草复合系统细根空间分布及地下竞争

采用田间分层挖掘法和图像扫描分析法,研究油茶-鼠茅草复合系统中油茶与鼠茅草细根生物量及形态空间分布,并用Levins提出的生态位重叠公式计算了油茶与鼠茅草种间的地下竞争指数。结果表明:油茶和鼠茅草细根(≤1 mm)的平均生物量分别是0.52和0.38 mg·cm-3,油茶细根生物量是鼠茅草的1.37倍;在水平方向上,油茶细根生物量整体趋势随着距树干距离增加而下降,而油茶细根的根长密度与比根长随着距树干距离的增加而升高;鼠茅草的细根生物量整体趋势随着距树干距离增加先升高后下降,根长密度及比根长都分布比较均匀;不同水平距离鼠茅草的根长密度均大于油茶,除距树干90 cm外,油茶细根生物量与竞争指数均大于鼠茅草;在垂直方向上,油茶细根生物量是随着土层加深先升高再下降,根长密度随着土层的加深而升高,比根长分布均匀;鼠茅草的细根生物量及根长密度均随着土层的加深而下降,而比根长则随着土层深度增加而上升;除0~10 cm土层外,油茶细根生物量与竞争指数均大于鼠茅草。在油茶-鼠茅草复合系统中,油茶根系遭遇鼠茅草根系的竞争,作为生存策略,为了避开这种竞争,最大限度地获取土壤中的资源,其根系产生了各种可塑性反应。     

供肥对小麦间作蚕豆群体产量及根系的调控

利用田间,池栽,盆栽等方法,对不同N,P水平下小麦间作蚕豆群体根系的时空分布及产量效应进行了研究。结果表明,供P对小麦-蚕豆间作系统有明显的增产作用,与不供P相比,田间试验中供P处理间作小麦和蚕豆分别提高了48.39%和16.69%,池栽试验中群体产量增产幅度为20.07%-43.14%。间作蚕豆经济产量增幅为58.46%-78.78%,小麦间作蚕豆多作系统2种作物根密度生长高峰期交错出现,小麦的峰值出现早于蚕豆,其中,小麦和蚕豆根干重最大值分别出现在抽穗期和成熟期,而根长的最大值分别出现在拔节期和成熟期,这在一定程度上减轻了共生期2种作物对水肥的竞争,也是此群体增产增效的原因之一,施P处理间作小麦的根重,根长和根表面积分别比不施P处理提高54.33%,48.88%和47.00%;施N处理间作小麦的根重,根长和根表面积分别比不施N的增加15.25%,11.61%和11.46%。间作小麦根重的57.61%和蚕豆的69.20%分布在0-30cm土层,随施P水平的提高,总根干重及根密度都趋于增加,且深层土壤中根系增加明显。     

华北低丘山区果药复合系统种间水分利用策略

了解林农复合系统的种间水分关系至关重要.该文通过稳定氘同位素研究了华北低丘山区核桃(Juglans regia)-菘蓝(Isatis tinctoria)/决明(Senna tora)复合系统各组分的水分来源, 试图明确该果药复合系统的种间水分利用策略, 为该区林农配置模式的选择提供理论依据.研究结果表明: 果药复合系统的土壤含水量明显高于单作菘蓝和单作决明地块, 在2012年,2013年上半年比单作菘蓝高26.74%和7.93%, 在下半年比单作决明高17.39%和13.65%.在果药复合系统内部, 土壤含水量以核桃树行中间位置的最低,树行北侧和树下最高.在各个土层深度, 单作系统的土壤水氢稳定同位素比率(δD值)均比复合系统的高.在菘蓝生长时期的春旱期, 复合系统中核桃的大部分水分来源于30-80 cm深层土壤水, 表明此时期核桃表层根系活性不高; 而决明生长时期正值雨季, 此时核桃优先利用雨水补充的0-30 cm浅层土壤水,表层根系活性增强.在任何生长时期, 菘蓝和决明85%以上的水分都来自浅层土壤水.在菘蓝苗期, 其根系尚未扎入深层土壤中, 单作菘蓝的水分完全来源于浅层土壤, 而在2012年间作菘蓝却有5.7%的水分来自于深层土壤, 在更为干旱的2013年该比例上升到9.7%, 该结果证实了核桃在旱季存在"水力提升"作用, 供浅根系作物吸收利用, 并且越干旱, 该水力提升作用越强.在华北低丘山区核桃-菘蓝/决明复合系统中, 深根性核桃改善了复合系统的土壤水分状况, 在旱季主要利用深层土壤水以避开与浅层作物的水分竞争,并能将深层土壤水提升至浅层土壤供菘蓝吸收利用, 核桃与两种药材表现为水分互利关系, 因而该模式适合在该地区发展.     

间套种植复合群体根系时空分布特征

选择小麦／大豆和玉米／甘蓝2种典型间套种植模式,探讨了复合群体根系营养竞争与补偿的生态学机制．结果表明,小麦／大豆复合群体根系生长在年生长期内显示出双峰交错性,小麦总根重峰值出现在6月初,而大豆峰值出现在8月上、中旬．根重与根长密度的生长还表现出异步性,根重峰值的出现早于根长．复合群体各配对作物根系的垂直分布呈层次递减性,玉米拔节前根重的85％以上都分布于0～20cm土层,且垂直生长呈多波顾次递推特点．间套作物根系的分布呈明显的“偏态”不均衡分布,套作玉米根系偏甘蓝行20．4～40．7cm,而甘蓝根系偏玉米行仅8．5～12．6cm．施肥使套作玉米与甘蓝根系的交叉幅宽由40．2cm下降到20．1cm,2种作物根系的交叉点位置由20．5cm上升到12．4cm．     

不同根系分隔方式对栗和茶幼苗生长的影响

研究不同根系分隔方式对栗(Castanea mollissima)/茶(Camellia sinensis)间作地下部分相互作用和植物种间互作动态的影响, 探究根系互作对植株株高、基径和根系生长的影响, 可为栗/茶复合经营模式的可持续发展提供科学指导。该研究以栗/茶间作和相应单作为研究对象, 运用盆栽实验的根系分隔技术(塑料膜分隔、尼龙网分隔和不分隔), 分别利用logistic生长模型模拟栗和茶株高与基径生长动态过程, 利用幂函数研究株高-基径的异速生长关系, 并从细根发育角度分析地下部分相互作用对植物生长发育的影响。结果显示: 与单作茶相比, 间作茶塑料膜分隔方式地上部分、地下部分和总的干生物量以及根长、根表面积、根体积、分形丰度和直径为0.2-1.0 mm根的根长分别显著增加了357.1%、281.8%和345.2%以及74.3%、273.9%、244.8%、42.0%和382.4%。间作茶塑料膜分隔方式的株高渐进值比单作茶显著增加了30.9%, 尼龙网分隔方式的间作栗株高渐进值和基径渐进值比单作栗分别显著增加了21.9%和28.2%; 塑料膜分隔方式下间作茶株高达到最大增长速率的时间和间作栗的基径达到最大增长速率的时间比相应单作模式分别显著延迟了14和15天。不同处理中栗和茶的株高-基径异速生长均呈显著线性正相关关系, 且不分隔方式下间作栗和间作茶的株高-基径异速生长模型的斜率均表现为最小, 且均<1。结果表明, 栗和茶间作时, 栗地上部分通过遮阴促进茶幼苗侧根分枝数、细根根长和株高的生长来增加其干生物量累积, 但地下部分则表现为竞争作用, 且随着地下部分竞争作用的强度增加会逐渐抵消地上部分的促进作用, 最终植物种间相互作用表现为中性作用。     

Response of the wheat rhizosphere soil nematode community in wheat/walnut intercropping system in Xinjiang,Northwest China

Intercropping Persian walnut (Juglans regia L.) and wheat (Triticum aestivum L.) have been widely applied in the Xinjiang Uygur Autonomous Region in Northwest China as a means of reducing soil and water losses and improving both land-use efficiency and economic returns. To understand how changes in soil conditions and nematode community structure can contribute to the evaluation of wheat–walnut intercropping systems from the view of soil fauna, we studied the soil nematode community in wheat rhizosphere soil under both monoculture and intercropping systems for 2 years. The results showed that the pH and total nitrogen and organic matter contents in intercropping systems with walnut trees were decreased compared with those of system with wheat alone. The nematode communities differed significantly between intercropping and monoculture plots, e.g., Rhabditis and Dorylaimus were dominant only in monocultures, whereas Tylenchus was dominant only in intercropping systems. Moreover, intercropping systems resulted in decreased nematode abundance, increased proportions of plant-feeding nematodes, and decreased omnivores/predators, particularly in the second year (2012). The decrease in diversity indices (H′) and ecological indices (WI, EI, and SI) of the nematode communities indicated high disturbance and low soil fertility in intercropping systems. Overall, wheat intercropping with walnut had a significant negative effect on wheat rhizosphere soil conditions.     

Interspecific water use strategies of a Juglans regia and Isatis tinctoria/Senna tora agroforestry

Aims Understanding the interspecific water relations is important for designing agroforestry systems. The objective of this study was to determine the water use strategies of component species in a walnut (Juglans regia)-woad (Isatis tinctoria)/sicklepod (Senna tora) agroforestry system.Methods Water sources of component species in a walnut-woad/sicklepod agroforestry system were investigated with the technique of stable deuterium isotope tracing at a site of hilly area in Northern China during 2012-2013.Important findings Results showed that the soil water content in the agroforestry system was 26.74% and 7.93% greater than in the pure woad field in the first half year, and 17.39% and 13.65% greater than in the pure sicklepod field in the second half year (sicklepod growth period), in 2012 and 2013, respectively. The lowest water content was found in the middle of tree rows, and the highest water content was found in the northern side of tree rows or under the trees. In the soil layers measured, the pure woad and pure sicklepod systems had greater hydrogen stable isotope ratios (δ D value) of soil water than in the agroforestry system. During the period of woad growth, more than half of the water absorbed by walnut was from the deeper soil layer (30-80 cm). In contrast, the walnut trees mainly utilized shallow layer (0-30 cm) soil water during the period of sicklepod growth. These findings suggest that walnut has a two-state root system: during the period of woad growth, shallow roots of walnut are not active when soil is dry whereas the sicklepod growth occur in rainy season, and the shallow roots of walnut are active and utilize more shallow soil water supplemented by rainwater. More than 85% of water used by both the woad and the sicklepod were from the shallow layer soil. At the seedling stage, the roots of woad, cannot grow into the deeper soil layer, and the absorbed water is completely from the shallow layer in the pure woad system. However, 5.7% of the water absorbed by the intercropped woad was from the deeper soil layer in 2012, and the proportion increased further (9.7%) in the following year when there was less precipitation. The results confirmed that hydraulic lift effect of walnut occurred on shallow layer crop in dry season, and this effect become greater under drier conditions. Therefore, deeper roots of walnut improved water condition in the walnut- woad/sicklepod agroforestry systems compared to pure crop systems. The walnut mainly utilized water from the deeper layer to avoid water competition with the shallow layer. In the dry season, crops benefited from the water provided by walnut roots through hydraulic lift. Walnut and intercropped plants exhibited water facilitation in the agroforestry systems, suggesting that this configuration is a suitable practice in this area.     

Effects of water supply on root traits and biological yield of Durum (Triticum durum Desf.) and Khorasan (Triticum turanicum Jakubz) wheat

The ability of a plant to change its root characteristics to increase the acquisition of soil water is an important adaptation mechanism to water limitation. In this regard, a field study was carried out in the Pannonian region of eastern Austria with two tetraploid wheat genotypes, i.e. Durum (Triticum durum Desf.) and Khorasan (Triticum turanicum Jakubz), during a comparatively wetter and drier year, i.e. 2008 and 2009, respectively. The genotypes showed significant differences in average root diameter and fine root length. All root traits varied with soil depth. The highest root length density and root biomass were observed with Khorasan wheat in 0–10 cm soil depth. Durum wheat showed a stronger response in fine roots to water availability and produced more fine roots in the moist year. Electric root capacitance was higher with Khorasan wheat. Durum showed higher biological yield stability across years with different precipitation with respect to above- and belowground biomass. It produced more leaf area under humid conditions. Khorasan allocated more assimilates to belowground organs in dry conditions, but without positive effect on aboveground biomass.     

Root length and biomass losses during sample preparation with different screen mesh sizes

Data are presented on the differences in root length density (RLD), dry matter (DM), and root diameter values determined on wheat and faba bean using sieves of different mesh size to separate roots from soil during sample preparation. Screens with 0.2, 1, and 2 mm (0.04, 1, and 4 mm²) aperture were used. Roots collected on the 2-mm sieve represented on average 55% of the weight and only 10% of the total length collected using a 0.2-mm sieve. With a 1-mm sieve 75% of weight was retained, but only 34% of the length. In the 0–20 cm soil layer average RLD and DM values ranged between 1.3 and 2.5 cm cm^-3 and 215 and 136 g m^-2 for faba bean and wheat respectively with 2 mm screens and 14.6 and 18.1 cm cm^-3 and 313 and 202 g m^-2 with 0.2 mm sieves. RLD was more affected than weight since losses from coarse screens were largely due to fine root fractions, although the 1-and 2-mm screens retained a small amount of fine roots that were long or attached to main structures. Variability was higher for measurements on coarser screens. The use of screens much coarser than the diameter of fine roots is not recommended for the study of surface-related phenomena in which root length quantification is necessary, while it may be acceptable for gross comparisons of root weight and spatial extent.     

Competition in tree row agroforestry systems. 1. Distribution and dynamics of fine root length and biomass

Complementarity in the distribution of tree and crop root systems is important to minimise competition for resources whilst maximising resource use in agroforestry systems. A field study was conducted on a kaolinitic Oxisol in the sub-humid highlands of western Kenya to compare the distribution and dynamics of root length and biomass of a 3-year-old Grevillea robusta A. Cunn. ex R. Br. (grevillea) tree row and a 3-year-old Senna spectabilis DC. (senna) hedgerow grown with Zea mays L. (maize). Tree roots were sampled to a 300 cm depth and 525 cm distance from the tree rows, both before and after maize cropping. Maize roots were sampled at two distances from the tree rows (75–150 cm and 450–525 cm) to a maximum depth of 180 cm, at three developmental stages. The mean root length density (L_rv) of the trees in the upper 15 cm was 0.55 cm cm⁻³ for grevillea and 1.44 cm cm⁻³ for senna, at the start of the cropping season. The L_rv of senna decreased at every depth during the cropping season, whereas the L_rv of grevillea only decreased in the crop rooting zone. The fine root length of the trees decreased by about 35% for grevillea and 65% for senna, because of maize competition, manual weeding, seasonal senescence or pruning regime (senna). At anthesis, the L_rv of maize in the upper 15 cm was between 0.8 and 1.5 cm cm⁻³. Maize root length decreased with greater proximity to the tree rows, potentially reducing its ability to compete for soil resources. However, the specific root length (m g⁻¹) of maize was about twice that of the trees, so may have had a competitive uptake advantage even when tree root length was greater. Differences in maize fine root length and biomass suggest that competition for soil resources and hence fine root length may have been more important for maize grown with senna than grevillea. This revised version was published online in June 2006 with corrections to the Cover Date.     

Fibrous carrot root responses to irrigation and compaction of sandy and organic soils

Field experiments were performed in Southern Finland on fine sand and organic soil in 1990 and 1991 to study carrot roots. Fall ploughed land was loosened by rotary harrowing to a depth of 20 cm or compacted under moist conditions to a depth of 25–30 cm by three passes of adjacent wheel tracks with a tractor weighing 3 Mg, in April were contiguously applied across the plot before seed bed preparation. Sprinkler irrigation (30 mm) was applied to fine sand when moisture in the 0–15 cm range of soil depth was 50% of plant-available water capacity. For root sampling, polyvinyl chloride (PVC) cylinders (30 × 60 cm) were installed in the rows of experimental plots after sowing, and removed at harvest. Six carrot plants were grown in each of in these soil colums in situ in the field.Fine root length and width were quantified by image analysis. Root length density (RLD) per plant was 0.2–1.0 cm cm^-3 in the 0–30 cm range. The fibrous root system of one carrot had total root lengths of 130–150 m in loose fine sand and 180–200 m in compacted fine sand. More roots were observed in irrigated than non-irrigated soils. In the 0–50 cm range of organic soil, 230–250 m of root length were removed from loosened organic soils and 240–300 m from compacted soils. Specific root surface area (surface area divided by dry root weight) of a carrot fibrous root system averaged 1500–2000 cm² g^-1. Root length to weight ratios of 250–350 m g^-1 effectively compare with the ratios of other species.Fibrous root growth was stimulated by soil compaction or irrigation to a depth of 30 cm, in both the fine sand and organic soils, suggesting better soil water supply in compacted than in loosened soils. Soil compaction increased root diameters more in fine sand than it did in organic soil. Most of the root length in loosened soils (fine sand 90%, organic soil 80%) and compacted soils (fine sand 80%, organic soil 75%) was composed of roots with diameters of approximately 0.15 mm. With respect to dry weight, length, surface area and volume of the fibrous root system, all the measurements gave significant resposes to irrigation and soil compaction. Total root volumes in the 0–50 cm of soil were 4.3 cm³ and 9.8 cm³ in loosened fine sand and organic soils, respectively, and 6.7 cm³ and 13.4 cm³ in compacted sand and organic soils, respectively. In fine sand, irrigation increased the volume from 4.8 to 6.3 cm³.