沙地赤松光合及叶绿素a快相荧光动力学特性

Photosynthetic characteristics and chlorophyll a fluorescence induction parameters of Pinus densiflora on sandy soil

沙地赤松在科尔沁沙地南缘区已有50a的引种历史,但对其生长表现还知之甚少,对其光合生理还一无所知。为深入了解其光合生理特性及机理,以同龄樟子松为对照,对沙地赤松成熟林分生长指标以及光合和叶绿素a快相荧光动力学特性进行了研究。结果表明:与樟子松相比,成林阶段沙地赤松具有较大的生长量、生物量,这与其较强的光合作用密切相关。沙地赤松最大净光合速率P_(max)(10.376μmol CO_2m^(-2)s^(-1))和平均净光合速率P_n(4.902μmol CO_2m^(-2)s^(-1))均高于樟子松,且具有较高的光饱和点LSP和较低的光补偿点LCP。暗呼吸速率(R_d)较低,导致其光合效率(P_(max)/R_d)较高。JIP-测定揭示了沙地赤松较强光合作用的内在机制,在O相至P相范围内,其相对可变荧光值(V_t)总体较低,说明其在电子传递过程中耗散能量较低,而用于光化学的能量较高。比活性参数进一步表明沙地赤松单位激发态面积反应中心数目(RC/CSo、RC/CSm)、吸收的光量(ABS/CSo、ABS/CSm)、被反应中心捕获的光量(TRo/CSo)、用于电子传递的能量均较高(ETo/CSo),也因此具有较高的性能指数,其PI_((ABS/CSo/CSm))分别是樟子松的1.42、1.65和1.63倍。显然在沙地环境下沙地赤松生长表现和光合性能优于樟子松,研究结果为扩大该树种在沙地上的引种栽培提供了初步的理论依据。

Pinus densiflora has grown in the southern Horqin Sandy Land,China,for 50 years,but little is known about its field performance in this region,and nothing is known about its photosynthetic physiology.To understand the physiological characteristics and mechanisms of photosynthesis in P.densiflora,mature trees were compared with the same-aged trees of Pinus sylvestris var.mongolica（the control）,and the growth characteristics of both species were investigated.Photosynthetic characteristics were analyzed with a Li-6400 system,and fast chlorophyll a fluorescence transients（OJIP）were analyzed with a Pocket PEA plant efficiency analyzer.Growth and biomass of mature P.densiflora was greater than that of P.sylvestris var.mongolica.This was closely related to stronger photosynthesis in P.densiflora,including a higher maximum net photosynthetic rate（Pmax,10.376 μmol CO2m-2s-1） and a large range of light adaptation with high light saturation point and low light compensation point.The dark respiration rate（Rd） of P.densiflora was low,leading to higher photosynthetic efficiency（Pmax/Rd）.Diurnal changes in the net photosynthetic rate（Pn） of P.densiflora ranged from 3.290 to 7.349 μmol CO2m-2s-1,and the mean Pnwas 4.902 μmol CO2m-2s-1,which was 36.2% higher than that of P.sylvestris var.mongolica.The Pnof P.densiflora at each time point was significantly higher than that of P.sylvestris var.mongolica,except at 14：00 and 16：00.The transpiration rate of P.densiflora was 34.8% lower than that of P.sylvestris var.mongolica,and its water use efficiency was 2.06-fold greater than that of P.sylvestris var.mongolica.The Pnof P.densiflora remained high when stomatal conductance was low.Compared with P.sylvestris var.mongolica,P.densiflora was less susceptible to dynamic photoinhibition,showing slight photoinhibition only at a PPFD of 2000 μmol m-2s-1,when Pnwas 91.4% of the maximum.The chlorophyll content in P.densiflora needles was 1.380 mg/g,double that in needles of P.sylvestris var.mongolica.The JIP test was used to reveal the mechanism for the strong photosynthesis of P.densiflora and showed that in the range from O to P phase,the relative variable fluorescence value of P.densiflora was generally low.This low value indicated that little energy was dissipated via the electron transfer chain,so that more energy could be used for photochemistry.The two species reached fluorescence maxima at different times under saturating illumination：700 ms for P.densiflora and 900 ms for P.sylvestris var.mongolica.The phenomenological energy fluxes per excited cross section（CS）were calculated;these indexes showed that,compared with P.sylvestris var.mongolica,P.densiflora had a higher density of reaction centers（RC/CSo,RC/CSm）,a greater proportion of photon flux absorbed by the antenna pigments（ABS/CSo,ABS/CSm）,higher trapping flux to the reaction center（TRo/CSo）,and used more energy for electron transfer（ETo/CSo）.These attributes led to its higher performance indexes.The PI（ABS/CSo/CSm）of P.densiflora were 1.42-,1.65-,and1.63-fold those of P.sylvestris var.mongolica,respectively.Together,these results suggest that the growth and photosynthetic performance of P.densiflora are better than those of P.sylvestris var.mongolica in the Horqin Sandy Land environment.This conclusion provides the theoretical basis for the expansion of P.densiflora cultivation in this region.