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IPCC报告显示,在2030—2052年,全球平均气温将比工业革命前提高1.5℃,气候变暖引发的干旱、高温等极端气候事件将对森林生态系统产生巨大影响。于健等[1]与赵学鹏等[2]研究发现,气候持续变暖对长白山树木径向生长及地理分布范围产生较大影响。理清树木生长对气候变化的响应机制,有利于制定合理的森林经营对策。树轮包含了树木生命周期中的气候信息,是分析气候变化的重要材料;然而,随着树轮-气候响应研究的深入,国内外学者对美国[3]、匈牙利[4]和新疆天山[5]等地区不同树种生长研究发现,轮宽对气候因子敏感性降低,利用其对气候进行重建会出现偏差,而树轮中的稳定碳同位素(δ13C)组成可以准确反映大气的13C/12C变化,对气候因子响应比轮宽更敏感[6]。将轮宽和稳定碳同位素综合分析有助于解释树木生长和长期水碳平衡与气候变化的关系,国内外学者依据树轮中的δ13C来推导年际水分利用效率,研究了瑞士石松(Pinus cembra L.)[7]和川西云杉(Picea likiangensis var. balfouriana (Rehd. et Wils.) Hillier ex Slsvin)[8]的水分利用效率对气候的响应,但同一树种对不同地点气象因子的响应可能不同。为了更好地理解植物对气候变化的生理响应过程,需要进一步加强对同一树种内在水分利用效率(WUEi)空间变异及关键影响因子响应的研究。
刺槐(Robinia pseudoacacia L.)为豆科、刺槐属植物,其根系浅而发达,适应性强,为我国水土保持和植被恢复的先锋树种,但受不同地点环境条件的影响,导致其生长差别较大,适应环境的刺槐生长较好,反之,则出现枯梢和退化等现象。先前研究发现,黄土高原刺槐径向生长与年均温度[9]和帕默尔干旱指数(PDSI)[10]显著正相关,但主要分析了刺槐生长与气候的关系,而对刺槐水碳利用与气候因子的关系认识不足。刺槐对环境的响应是一个长期过程,需在水碳方面保持相对平衡,WUEi是碳同化速率与气孔导度的比值,将水碳耦合在一起,能够解释树木在年际尺度上对气候变化的生理响应机制[11]。因此,本研究以河南省民权县与陕西省白水县两地林龄相近的刺槐林为研究对象,通过测定轮宽与δ13C,计算胸高断面积增量(BAI)和WUEi,回溯性分析不同地点刺槐径向生长和水分利用对气候因子响应的差异,确定影响刺槐生长和水分利用效率的主导气候因子,理清不同地点刺槐水碳利用对气候因子响应的差异,为今后气候变化背景下刺槐人工林的树种更新、结构优化和营林管理等提供参考。
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以国际树木年轮数据库(ITRDB)为采样准则[12],于2020年6月在民权县国营民权林场和白水县新卓国有林场分别随机设置6块20 m × 20 m样方,测定刺槐胸径、树高、郁闭度等指标(表1),民权与白水的刺槐林龄相近,密度相差约10%,且民权刺槐树高与胸径均大于白水。使用生长锥在两地随机选取生长状况良好的100株刺槐钻取树芯,每株沿东西、南北方向各取1根,待样芯自然晾干后使用不同目数的砂纸进行打磨,直至样芯年轮清晰可见。
表 1 样地情况统计
Table 1. Statistical description of plots.
样地
Sample
plots经度(E)
Longitude纬度(N)
Latitude海拔/m
Altitude样树/样芯
Tree/Cores时间
Time
span树龄/a
Stand
age平均树高/m
Average
height平均胸径/cm
Average
DBH郁闭度/%
Canopy
density密度 / (株·hm−2)
Density民权MQ 115°4′48″ 34°43′54″ 90 77/154 1981—2018 38 17.2±1.2 35.95±1.1 0.64±0.2 896±66 白水BS 109°22′3″ 35°16′56″ 1 210 80/160 1979—2018 40 14.6±1.5 28.65±1.3 0.73±0.1 983±41 -
使用Lintab 6年轮分析仪(Rinntech公司,德国)与TASP-Win软件测定样品轮宽并进行交叉定年,精确至0.01 mm;使用COFECHA、ARSTAN程序构建刺槐年表[13],最终民权与白水两个样地分别选用154、160根样芯制作年表。经对比发现,剔除生长趋势及非气候信息的干扰后,标准化年表(STD)中保留较多的低频气候信息,因此,本文选用标准化年表指数对刺槐径向生长进行分析。胸高断面积增量(BAI,cm2)能较好反映树木生长量大小,用轮宽数据计算:
$ BAI = {\rm{\pi }}\left( {{R^2}_n - {R^2}_{n - 1}} \right) $
(1) 式(1)中:R为树木半径/cm,n为年轮形成年份。
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已有研究证实,选取4棵树的4根样芯测定δ13C,结果基本可代表研究区δ13C的绝对含量和变化趋势[14]。因此,从两地各选取4根年轮清晰的样品逐年剥离,进行称量、烘干、粉碎及过筛等步骤后放入TOC(Elementar Analysensysteme,德国)内充分燃烧,利用气体混合仪(Li-6000,中国)及LGR CO2同位素测定仪(LGR-912,美国)测量δ13C值,每30样品插入一个标准样进行校准,测定精度0.1‰,δ13C值采用维也纳白垩系皮狄组地层内美洲拟箭石(VPDB)标准,计算公式如下[15]:
$ {\delta ^{13}}{\rm{C = }}\left( {\frac{{{R_{sample}}}}{{{R_{stan dard}}}} - 1} \right) \times 1\;000{\text{‰}} $
(2) 式(2)中:Rsample和Rstandard为样品与标准物13C /12C的摩尔比率。
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为避免树轮δ13C记录气候信息受工业革命影响,依据McCarrol与NOAA的方法对其进行校正[16],树轮中稳定碳同位素辨别值(Δ13C)可由Farquhar[17]等公式计算:
$ {\varDelta ^{13}}{\rm{C = }}\left( {\frac{{{\delta ^{13}}{{\rm{C}}_{{\rm{atm}}}} - {\delta ^{13}}{{\rm{C}}_{{\rm{tree}}}}}}{{1 + {\delta ^{13}}{{\rm{C}}_{{\rm{tree}}}}/1\;000}}} \right) $
(3) 式(3)中:δ13Catm、δ13Ctree分别为大气δ13C值和树轮中δ13C值;对C3植物,Δ13C与胞间CO2浓度(Ca)和大气CO2浓度(Ci)线性关系有关[18],WUEi可通过Δ13C与Ca值之间的关系计算获得[19]
$ WU{E_i} = \frac{{{C_a}\left( {b - {\varDelta ^{13}}{\rm{C}}} \right)}}{{1.6\left( {b - a} \right)}} $
(4) 式(4)中:数值1.6为水蒸汽和CO2在空气中扩散比率,a = 4.4‰,b = 27‰,分别表示CO2扩散及羧化过程的同位素分馏系数。
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气象数据来自国家气象局,民权与白水气象数据分别采用离采样点较近的商丘气象站(34°27′ N,115°40′ E,海拔50.1 m)和洛川气象站(35°49′ N,109°30′ E,海拔1 159.8 m),干旱指数(SPEI)使用软件SPEI计算[20]。本文使用SPSS完成Pearson相关分析,R语言软件绘制Pearson相关关系图,AMOS.22(IBM,美国)建立结构方程模型。
河南民权与陕西白水刺槐径向生长与水分利用效率对气候响应的差异
Differences in the Response of Radial Growth and Intrinsic Water Use Efficiency of Robinia pseudoacacia to Climatic Factors in Minquan of He'nan Province and Baishui of Shaanxi Province
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摘要:
目的 分析不同地区刺槐径向生长、内在水分利用效率(WUEi)对气候因子响应的差异,确定影响其生长和水分利用的主导因子,为我国刺槐人工林在气候变化背景下的管理经营提供参考。 方法 在河南民权(MQ)与陕西白水(BS)两地,利用树木年代学方法建立刺槐轮宽年表,测定树轮稳定碳同位素值(δ13C),计算刺槐年际间的WUEi,结合气象资料分析刺槐径向生长与WUEi对气候响应的差异。 结果 两地刺槐林龄相似且民权刺槐轮宽随着林龄的增加呈线性下降趋势,白水呈“升-降”曲线变化。两地刺槐的胸高断面积增量(BAI)变化趋势相似,均呈“升-降”的曲线。民权刺槐的δ13C和WUEi均低于白水刺槐。Pearson相关结果显示:月尺度上,两地刺槐标准化年表(STD)指数主要与夏季降水和干旱指数(SPEI)显著正相关(P < 0.05),且白水刺槐与上年11月平均降水、SPEI显著负相关(P < 0.05);民权刺槐WUEi与当年3月和8月的平均温度、最高温度显著正相关(P < 0.05),白水刺槐WUEi与当年3、4月、上年及当年6、7月平均温度、最高温度和最低温度显著正相关(P < 0.05)。路径分析模型表明,年尺度上,白水县刺槐STD指数与平均降水、平均温度存在显著正效应(P < 0.05),而民权刺槐对气候因子响应不显著;两地刺槐WUEi均与平均温度存在显著正效应(P < 0.05)。 结论 平均降水是两地刺槐径向生长的主导因子,白水刺槐生长对平均降水的敏感性高于民权刺槐,平均温度是两地刺槐WUEi的主导因子,白水刺槐WUEi较民权刺槐对温度变化更敏感。 Abstract:Objective To analyze the response of radial growth and intrinsic water use efficiency (WUEi) of Robinia pseudoacacia to climate factors at different locations, and to determine the dominant factors affecting the growth and water use mechanism, so as to provide reference for the management of R. pseudoacacia plantations in China under climate change. Method The ring width chronologies were established in Minquan (MQ) of He'nan Province and Baishui (BS) of Shaanxi Province. The stable carbon isotopic composition (δ13C) of tree ring was measured to calculate the WUEi. The differences in the response of R. pseudoacacia to climatic variation were analyzed with meteorological data. Result The plantations at the two locations were in similar age. The tree-ring width at BS presented a trend of initially increasing and thereafter decreasing with the increase of tree age, whereas at MQ, the tree-ring width showed a linear decreasing trend with tree age increase. The trends of basal area increment (BAI) of R. pseudoacacia at the two locations were similar, presenting a trend of initially increasing and thereafter decreasing with the increase of tree age. The δ13C value and WUEi of the trees in MQ were lower than those of BS. The Pearson correlation results showed that on a monthly scale, the STD index of R. pseudoacacia in the two locations was mainly positively correlated with the summer precipitation and drought index (SPEI) (P < 0.05), and the R. pseudoacacia in BS was significantly negatively correlated with the average precipitation and SPEI in November of the previous year (P < 0.05). The WUEi of trees in MQ was significantly positively correlated with the average temperature and maximum temperature in March and August (P < 0.05), while that of trees in BS was significantly positively correlated with the average temperature, maximum temperature and minimum temperature from March to April of the current year, and June to July of the previous and current year (P < 0.05). The path analysis model showed that on the annual scale, the STD index of R. pseudoacacia in BS had a significant positive effect on the average precipitation and average temperature (P < 0.05), while the R. pseudoacacia in MQ had no significant response to climate factors. The annual average temperature had significantly positive effect on WUEi of trees at both the locations (P < 0.05). Conclusion The average precipitation is the dominant factor influencing the radial growth of R. pseudoacacia at both the locations, and the sensitivity of growth of trees in BS is higher than that of trees in MQ. The average temperature is the dominant factor influencing WUEi at the two locations, and the WUEi of trees in BS is more sensitive to the temperature than that of trees in MQ. -
表 1 样地情况统计
Table 1. Statistical description of plots.
样地
Sample
plots经度(E)
Longitude纬度(N)
Latitude海拔/m
Altitude样树/样芯
Tree/Cores时间
Time
span树龄/a
Stand
age平均树高/m
Average
height平均胸径/cm
Average
DBH郁闭度/%
Canopy
density密度 / (株·hm−2)
Density民权MQ 115°4′48″ 34°43′54″ 90 77/154 1981—2018 38 17.2±1.2 35.95±1.1 0.64±0.2 896±66 白水BS 109°22′3″ 35°16′56″ 1 210 80/160 1979—2018 40 14.6±1.5 28.65±1.3 0.73±0.1 983±41 -
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