摘要:为探明陇东旱塬苹果树根系年周期生长动态规律, 以及覆膜保墒措施下垂直土层根系数量、形态、分支特性、土壤理化性状的时空差异, 以18 a生苹果树(‘长富2号’/山定子)为试材, 于苹果根系3次发根高峰: 春季萌芽至新梢旺长前(Ⅰ)、新梢停长期(Ⅱ)和采果后至落叶期(Ⅲ), 采用土壤剖面法调查清耕(CK)、覆膜2 a (2Y)、覆膜4 a (4Y)和覆膜6 a (6Y)的根系空间分布, 并对根系生物量、根长、表面积、比根长、比分支数等进行测定, 探索不同覆膜年限处理下细根生长时空动态特征。借助回归统计分析, 阐明苹果树细根生长策略对覆膜年限的响应。结果表明: 在苹果根系生长年周期中, 第Ⅲ次发根高峰最为重要。各处理苹果细根在第Ⅲ次发根高峰的生物量占3次发根高峰期总生物量的73.55%~84.85%, 在第Ⅰ发根高峰表层土壤(0~20 cm)的细根分支数分别为第Ⅲ次发根高峰的130.67%、100.53%、156.63%和238.63%, 可提高原位土壤资源利用效率; 在第Ⅲ次发根高峰中, CK促进细根根长与根表面积在表层土壤中的分布, 分别为第Ⅰ次发根高峰的275.64%和248.96%; 并抑制细根分支, 分支数和比分支数仅为第Ⅰ次发根高峰的76.53%和14.68%, 以达到扩展有效营养空间、降低根系内部竞争的作用。短期覆膜(2Y)各土层的土壤含水量分别为CK的112.39%、118.04%、124.06%、133.59%和114.49%, 细根生物量在3次发根高峰中分别为CK的116.72%、232.35%和112.09%; 土壤表层细根比根长在第Ⅰ和Ⅲ次发根高峰相比CK分别提高47.1%和62.92%, 根表面积则分别提高67.21%和56.88%; 深层土壤(80~100 cm)细根分支数相比CK分别提高282.22%和7.27%。可见2Y处理可促进表层土壤细根形态性状的表达及深层土壤根系分支结构的建成, 细根均匀分布于垂直土层0~100 cm的距干0~120 cm范围内。6Y处理在年生长初期表层土壤的细根分支数和比分支数相比CK分别提高6.11%和34.6%, 而在年生长后期则仅为CK的58.1%和19.56%, 呈年生长初期重分支、年生长后期简化分支的构型特点, 并显著抑制第Ⅲ次发根高峰细根生长, 深层土壤的细根根长、根表面积和比根长仅为CK的35.19%、40.43%和82.67%。即苹果细根生长受物候期和树体营养周转的影响, 在年生长初期应用“资源保守获取型”生长策略, 在年生长后期采取“资源快速获取型”生长策略; 短期覆膜(2Y)可改善土壤理化性状, 促进细根拓展延伸范围; 长期覆膜(6Y)对亚表层土壤(20~40 cm)的破坏作用, 阻碍细根下扎, 集中土壤表层分布。
关键词:苹果/
覆膜/
细根特征/
适应策略
Abstract:This study investigated the annual growth dynamics of apple tree roots in the dry plateau of Longdong and the temporal and spatial differences in the number, morphology, branching characteristics of the roots, and soil physical and chemical properties in vertical soil layers under film mulching and soil moisture conservation measures. Eighteenth-year-old apple trees (‘ Nagano Fuji No.2’) were assessed three times in the rooting peak times of apple tree: from spring sprouting to vigorous growth of new shoots (Ⅰ), shoots stopped growing (Ⅱ), and from fruit harvest to defoliation (Ⅲ). Using the soil profile and stratified sampling method, different treatments (conventional tillage [CK], film-mulching for two years [2Y], film-mulching for four years [4Y], and film-mulching for six years [6Y]) were investigated to analyze the spatial distribution of biomass, root length, surface area, specific root length, and the specific branch (branch number/dry matter weigh) of roots. Regression analysis was used to assess the fine root growth strategy for apple trees with plastic film mulching. The results showed that the rooting peak Ⅲ was the most important stage of the annual growth cycle of apple roots. The fine roots biomass at rooting peak Ⅲ under each treatment was 73.55%–84.85% of the total biomass at the three rooting peaks. The number of fine root branches at rooting peak Ⅰ in the surface soil (0–20 cm) was 130.67%, 100.53%, 156.63%, and 238.63% of that at rooting peak Ⅲ, which effectively improved the utilization of the soil resources in situ. At rooting peak Ⅲ, CK promoted the distribution of fine root length and root surface area in the surface soil, which were 275.64% and 248.96% of those at rooting peak Ⅰ, respectively. The number of branches and specific branches were only 76.53% and 14.68% of those at rooting peak Ⅰ, which expanded the effective nutrient space and reduced the internal competition of the root system. The soil water content in the short-term mulching (2Y) treatment in each soil layer were 112.39% (0?20 cm), 118.04% (20?40 cm), 124.06% (40?60 cm), 133.59% (60?80 cm), and 114.49% (80?100 cm) of CK; and the fine root biomass was 116.72%, 232.35%, and 112.09% of CK at the three rooting peak times. Compared with CK, the specific root length of the surface fine roots increased by 47.1% and 62.92% at rooting peaks Ⅰ and Ⅲ, and the root surface area increased by 67.21% and 56.88% in 2Y treatment. The number of fine root branches in the deep soil (80–100 cm) increased by 282.22% and 7.27%, respectively, compared with CK. The 2Y treatment promoted fine root morphological trait expression at the surface soil and branch structure establishment in the deep soil. Fine roots were evenly distributed in the 0–100 cm vertical soil layer and 0–120 cm horizontally from tree. Compared with CK, the 6Y treatment increased the number of fine root branches and specific branches by 6.11% and 34.6%, respectively, in the early growth stage, but by 58.1% and 19.56% in the late growth stage. These results demonstrate the characteristics of complex branches in the early growth stage and simplified branches in the late growth stage significantly inhibit the growth of fine roots at rooting peak Ⅲ. The fine root length, root surface area, and specific root length in the deep soil were 35.19%, 40.43%, and 82.67% of those of CK, respectively, in 6Y treatment. Fine root growth was affected by the phenological period and the turnover of tree nutrients; the “conservatively obtaining resources” growth strategy was applied in the early growth stage, and the “rapidly obtaining resources” growth strategy was adopted in the late growth stage. Short-term film mulching (2Y) can improve the physical and chemical properties of the soil and promote fine root extension. Damage from long-term plastic film mulching (6Y) to the subsurface soil (20–40 cm) prevented the fine roots from settling down and they became concentrated in the surface layer.
Key words:Apple/
Film-mulching/
Characteristics of fine root/
Adaptation strategy
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