准噶尔荒漠分布的早春短命植物不仅具有十分独特的生物学特点,而且在荒漠植物群落演替、物种多样性维持及土壤改良与防治水土流失等方面具有重要的生态学价值。该文运用Li-6400开放式气体交换光合作用测定系统,对分布于准噶尔荒漠的16种早春短命植物生长盛期的净光合速率(P_n)、蒸腾速率(T_r)、水分利用效率(WUE)等特征进行了测定,并对其中7种植物与生长相关的生物量分配特征进行了分析。结果表明:1)16种植物的最大P_n、 最大T_r及WUE分别为8.07~35.96 μmol CO₂·m^-2·s^-1、3.16~29.64 mmol H₂O·m^-2·s^-1、0.54~4.26 μmol CO₂·mmol^-1H₂O;种间最大P_n与最大气孔导度(Stomatal conductance, G_s)之间存在正相关关系,其相关系数为0.77(p<0.05),线性回归斜率为26.36 μmol·mmol^-1;从光合速率对胞间CO₂浓度及光量子通量密度的响应曲线来看,这类植物的表观CO₂补偿点均在4~5 Pa之间(28~30 ℃),表观羧化效率为0.64~1.86 μmol CO₂·m^-2·s^-1·Pa^-1,表观量子效率为0.05~0.06。2)从生物量分配来看,所测植物的个体生物量为0.05~0.39 g;单株总叶面积为 3.24~51.40 cm²;单位叶面积干重为0.40~0.77 g·m^-2,根在总生物量中所占比例为5.72%~19.43%,单株叶面积比在2.92~9.00 m²·kg^-1之间。种间根所占生物量的比与对应的WUE之间的比较分析结果表明,二者之间存在显著的正相关关系,其相关系数r为0.93(p<0.01)。这些结果表明,所观测的早春短命植物具有典型的C₃植物特征,相比其它类型的荒漠植物具有较高的单位叶面积P_n、高T_r及低WUE,并且在生长发育过程中表现出很低的根/地上生物量比、较高的叶面积比和单位叶面积干重,说明它们具有相对高的生长速率,这与其生长发育节律相一致,反映了它们与准噶尔荒漠环境相适应的特点。

Aims Spring ephemerals characterized by very short-term growth rhythm and specific biological traits in the Junggar Desert of China play an important role in succession of the desert plant community, maintenance of the desert biological diversity and conservation of water and soil in desert. The main aim of the present study was to address: 1) the photosynthetic characteristics and the biomass allocation traits of spring ephemerals and 2) the relationship between these traits and unique growth pattern of these spring ephemerals.

Methods In vivo photosynthetic traits of 16 spring ephemerals at their growth stages were measured by an open gas-exchange measurement system (Li-6400) and biomass allocation patterns were measured in seven species.

Important findings Maximum net photosynthesis rate (P_nmax),maximum transpiration rate (T_rmax) and water use efficiency (WUE) of 16 species were 8.07~35.96 μmol CO₂·m^-2·s^-1, 3.16~29.64 mmol H₂O·m^-2·s^-1 and 0.54~ 4.26 μmol CO₂·mmol^-1H₂O, respectively. P_nmax was positively correlated with maximum stomatal conductance, the correlation coefficient was 0.77 (p<0.05) and the slope in the linear region was 26.36 μmol·mmol^-1. Based on analysis for the response of P_n to internal CO₂ concentration and to photosynthetic photon flux density, apparent CO₂ compensation point are in the range of 4 to 5 Pa (ambient air temperature of 28~30 ℃ during the measurement), apparent carboxylation efficiency ranged from 0.64 to 1.86 μmol CO₂·m^-2·s^-1·Pa^-1, and apparent quantum yield ranged from 0.05 to 0.06. Biomass allocation data analysis showed that individual biomass of spring ephemerals were very low (0.05~0.39 g). Total leaf area ranged from 3.24 to 51.40 cm², leaf mass per unit leaf area ranged from 0.40 to 0.77 g·m^-2, root/total biomass ratio was 5.72%~19.43%, and leaf area ratio was 2.92~9.00 m²·kg^-1. The percentage of total biomass allocated to roots was positively correlated with WUE for the seven investigated species (r=0.93, p<0.01). Results indicate that the species investigated are typical C₃ plants. These spring ephemerals are characterized by higher P_n, T_r and lower WUE in comparison with other desert species. The unique biomass allocation of low root/aboveground biomass ratio, higher leaf area ratio, higher leaf mass per unit leaf area, and photosynthetic traits are involved in the physiological mechanisms that contributed to the rapid growth of desert spring ephemerals.