Tropical perennial grasses that can rapidly establish deep roots have a greater potential to survive soil surface drying sooner after establishment. This research aimed to identify species that establish deep roots quickly and to investigate the mechanisms that drove rapid vertical root development. Perennial grass species Brachiaria brizantha, Brachiaria decumbens, Brachiaria humidicola, Brachiaria hybrid Mulato II, Brachiaria mosambicensis, Panicum maximum, Setaria sphacelata and Cynodon dactylon were grown in rhizotrons that facilitated measurement of the rate of root depth development, the rate of root length development, photosynthesis and morphological traits. Principal component analysis was employed to separate grass species according to functional traits of vertical root development and their growth strategies. P. maximum established roots more rapidly to 50 cm depth than the other species examined and accumulated biomass and leaf area faster. It was differentiated from other species by a greater percentage of fine root length (< 0.2 mm diameter), a higher photosynthetic rate and ratio of root length to leaf area according to the principal component analysis. The growing degree days required for root establishment to 50 cm depth was negatively correlated with the percentage of fine root length, and positively correlated with root angle. The exponential rate of root depth development per growing degree day increased with average root diameter in B. humidicola and B. hybrid Mulato II, indicating a conservative growth strategy. Rapid vertical root development with a narrow root angle, higher photosynthetic rate, higher ratio of root length to leaf area and higher percentage of fine roots were apparent mechanisms that enabled P. maximum to establish deep roots faster than other species. P. maximum appears to be better able to avoid water stress during surface drying by accessing profile moisture. Greater average root diameter and percentage of root length with higher diameters was related to increased exponential rate of root depth development and wide root angle.

中文翻译：

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热带多年生牧草根深发育与根角、根径和叶面积有关

能够迅速扎根深根的热带多年生禾本科植物在扎根后较早地在土壤表面干燥中存活下来的潜力更大。这项研究旨在确定快速建立深根的物种，并调查推动垂直根系快速发育的机制。多年生草种 Brachiaria brizantha、Brachiaria decumbens、Brachiaria hypocumbens、Brachiaria hybrid Mulato II、Brachiaria mosambicensis、Panicum maximum、狗尾草和狗牙根在根茎中生长，有助于测量根深度发育速度、根长度发育速度、光合作用和形态特征。根据垂直根系发育的功能性状及其生长策略，采用主成分分析对草种进行分离。P。最大建立根比其他物种更快地达到 50 厘米深度，并且更快地积累生物量和叶面积。根据主成分分析，它与其他物种的区别在于细根长度的百分比更高（<0.2 毫米直径），更高的光合速率和根长度与叶面积的比率。生根至50 cm深度所需的生长期天数与细根长百分比呈负相关，与根角呈正相关。每生长度日根深度发育的指数速率随平均根直径的增加而增加，B.hydricola 和 B.hybridMulato II，表明保守的生长策略。根角窄，光合速率高，垂直根系发育快，更高的根长与叶面积比和更高的细根百分比是使最大的根比其他物种更快地建立深根的明显机制。P.maximum 似乎能够通过获取剖面水分更好地避免表面干燥过程中的水分压力。较大的平均根直径和较大直径的根长度百分比与根深度发育的指数速率增加和根角较宽有关。