| In order to understand the effects of different site preparation to carbon sequestration and water consumption characters of Eucalyptus urophylla×E. grandis(DH3229) plantation, three kinds of site preparation(no controlled burning and dig hole, no controlled burning and furrowing, controlled burning and full cultivation), with field investigation and indoor analysis, were conducted on 2.5-year-old E. urophylla×E.grandis(DH3229) plantation in Guangdong. The results are as follows:1. Growth characteristicsThe diameters of burning with full cultivation and furrowing were not significant difference but larger than dig hole obviously. In the short period of time(< 24 months), there are little difference between burning with full cultivation and furrowing for DBH growth/2 months, with dig hole least; DBH growth/2 months increased for furrowing, larger than the other two measures. Height growth of dig hole is slower than burning with full cultivation and furrowing, with height increment of three kinds of site preparation almost equal for small-month-old(< 16 months). Height growth rate of furrowing was better than the other two measures with age increase. The biomass allocation ratios are: trunk>root>branch>leaf. Different site preparation has no significant impacts on biomass allocation for different organs. The growth of E. urophylla×E.grandis was effected by a variety of meteorological and soil factors, among which rainfall and potential evaporation is the greatest. Rainfall had greater impact on E. urophylla×E.grandis with dig hole while potential evaporation with furrowing.2. Carbon storage and its distribution(1) The average carbon content in different organs of DH3229 ranges from 44.37% to 57.42%, with leaf > truck > branch > root > bark. No significant differences(P < 0.05) were observed in carbon content among the shrub, herb and litter layers of the DH3229 plantations under different site preparations. Carbon content in the soil layer(0-100 cm) decreased with site depth increasing.(2)The carbon storage of tree layer were 18.01 t/hm2(no controlled burning and dig hole), 30.49 t/hm2(no controlled burning and furrowing) and 23.56 t/hm2(controlled burning and full cultivation) respectively. Carbon storage in each organ is: stem > root > leaf > branch > bark. Except the bark, the carbon storage in other organs for three different site preparation is: furrowing > all reclamation > dig hole.(3) The total ecosystem carbon storage of DH3229 plantations was 144.77 t/hm2(dig hole), 197.03 t/hm2(burning) and 161.16 t/hm2(all reclamation site preparation), with soil layer > vegetable layer > litter layer. Carbon storage allocation for furrowing was the largest in tree and soil layers. The carbon storage of tree stratum and soil layer is in the majority of whole ecological system(> 93%). However, different combinations of site preparation have no significant effects on C storage allocations in the litter layer.3 The variation of soil water conditionThe spatio-temporal distribution of soil water under three different site preparation was different. Hole preparation is the highest for soil water, with full cultivation and furrowing taking second place in 2014. The soil water dynamic can be divided into consuming peried(April-June), accumulating period(July-September), lowering period(October-November) and stable period(December-next March). Soil water dynamics in vertical direction can be divided into variable greatly layer(0-20cm), mainly using layer(20-50cm), subactive using layer(50-90cm).Water content in the same soil layer under three site preparation measures was significantly different. The order of soil water content in 0-40 cm soil layer was furrowing > dig hole > burning and full cultivation. The soil water content under dig hole was highest of the deeper soil layer(40-80 cm), the soil water content under(40-60 cm layer) furrowing was higher than under burning and in 60-80 cm soil layer, the water content was higher under full cultivation.4 Rainfall and the interception of vegetation canopyThe evaporation in 2013 and 2014 were 1240.68 mm and 1078.49 mm, respectively while rainfall was 1678.3 mm and 1198.4 mm. The rainfall in 2013 was 40% and 49 times(mainly lightest rain<1.0 mm/h) more than in 2014 but the heavy rain in 2013 and 2014 showed no significant difference..The reject rate of E. urophylla×E.grandis was furrowing(21.54%) > burning and full cultivation(17.78%) > dig hole(16.82%). The reject rate of furrowing and dig hole were relatively stable. The throughfall and reject showed a non-linear correlation with throughfall.5 Transpiration of E. urophylla×E. grandis plantationsThe dynamic of sap flux density were consistent with solar radiation in different weather both of them presenting lag effect of sap flux density. In sunny days, sap flux density presented a regular single peak curve while a mutimodal curve in cloudy and rainy days. The sap flux density in cloudy and rainy days fluctuated significantly and less than that in sunny days. The daily variation of sap flux density was obvious, presenting an“start-activate-decrease” phenomenon. The sap flux density has a lower value during January to April.Photosynthetically active radiation was the most significant meteorological factor impacting the sap flux density(P<0.01) and other meteorological factors such as air tempreture, wind speed,air relative humidity and vapor pressure deficit were extremely significant with sap flux density, however, rainfall showed significantly negative correlation with sap flux density。The dynamic of sap flow flux were consistent with sap flux density under three site preparation measures. The individual daily/month sap flow flux and transpiration water consumption showed no significant difference under burning and full cultivation and furrowing, but both of them were significantly larger than that under dig hole.6. Water use efficiencyThe water use efficiency for biomass growth of single plant was followed as: furrowing(17.142 g/kg) > burning and full cultivation(14.13 g/kg) > dig hole(13.63 g/kg), and water use efficiency for carbon sequestration of single plant was furrowing(9.31 g/kg) > burning and full cultivation(7.04 g/kg) > dig hole(6.84 g/kg).Water use efficiency on biomass growth of plantation were as follows 4.05 g/kg(furrowing), 3.22 g/kg(burning and full cultivation), 1.94 g/kg(dig hole). The order of water use efficiency for carbon sequestration of plantation was 2.24 g/kg(furrowing) > 1.6 g/kg(burning and full cultivation) > 0.97 g/kg(dig hole). Furrowing has the highest water use efficiency, and was better than the other site preparation measures.Overall, furrowing had the highest carbon sequestration capacity and water use efficiency among three site preparation measures, burning and full cultivation is the second, and dig hole is the worst. Therefore, considering of the growth, carbon sequestration, water consumption and afforestation costs, we should take the furrowing site preparation. |
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