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1.
In an experimental site for reforestation of degraded area, three-year-old plants of Bertholletia excelsa Humb. & Bonpl. were subjected to different fertilization treatments: T0 = unfertilized control, T1 = green fertilization
(branches and leaves) and T2 = chemical fertilization. Higher net photosynthetic rates (P
N) were observed in T1 [13.2±1.0 μmol(CO2) m−2 s−1] compared to T2 [8.0±1.8 μmol(CO2) m−2 s−1] and T0 [4.8±1.3 μmol(CO2) m−2 s−1]. Stomatal conductance (g
s), transpiration rate (E) and water use efficiency (WUE) of individuals of T1 and T2 did not differ significantly, however, they were by 88, 55 and
63%, respectively, higher in T1 than in the control. The mean values of variable fluorescence (Fv), performance index (P.I.) and total chlorophyll [Chl (a+b)] were higher in T1. Our results indicate that green fertilization improves photosynthetic structure and function in plants
of B. excelsa in young phase. 相似文献
2.
The relationships between dark respiration rate (R
D) and net photosynthetic rate (P
N) in Quercus ilex L. shrubs growing at the Botanical Garden in Rome were analysed. Correlation analysis of the data sets collected in the year
2006 confirmed the dependence among the considered leaf traits, in particular, R
D was significantly (p<0.05) correlated with P
N (r = 0.40). R
D and P
N increased from March to May [1.40±0.10 and 10.1±1.8 μmol(CO2) m−2 s−1 mean values of the period, respectively], when air temperature was in the range 14.8–25.2 °C, underlining the highest metabolic
activity in the period of the maximum vegetative activity that favoured biomass accumulation. On the contrary, the highest
R
D [1.60±0.02 μmol(CO2) m−2 s−1], associated to the lowest P
N rates (44 % of the maximum) and carbon use efficiency (CUE) in July underlined the mobilization of stored material during
drought stress by a higher air temperature (32.7 °C). 相似文献
3.
Four temperature treatments were studied in the climate controlled growth chambers of the Georgia Envirotron: 25/20, 30/25,
35/30, and 40/35 °C during 14/10 h light/dark cycle. For the first growth stage (V3-5), the highest net photosynthetic rate
(P
N) of sweet corn was found for the lowest temperature of 28–34 μmol m−2 s−1 while the P
N for the highest temperature treatment was 50–60 % lower. We detected a gradual decline of about 1 P
N unit per 1 °C increase in temperature. Maximum transpiration rate (E) fluctuated between 0.36 and 0.54 mm h−1 (≈5.0–6.5 mm d−1) for the high temperature treatment and the minimum E fluctuated between 0.25 and 0.36 mm h−1 (≈3.5–5.0 mm d−1) for the low temperature treatment. Cumulative CO2 fixation of the 40/35 °C treatment was 33.7 g m−2 d−1 and it increased by about 50 % as temperature declined. The corresponding water use efficiency (WUE) decreased from 14 to
5 g(CO2) kg−1(H2O) for the lowest and highest temperature treatments, respectively. Three main factors affected WUE, P
N, and E of Zea: the high temperature which reduced P
N, vapor pressure deficit (VPD) that was directly related to E but did not affect P
N, and quasi stem conductance (QC) that was directly related to P
N but did not affect E. As a result, WUE of the 25/20 °C temperature treatment was almost three times larger than that of 40/35 °C temperature treatment. 相似文献
4.
The morphological, anatomical and physiological variations of leaf traits were analysed during Quercus ilex L. leaf expansion. The leaf water content (LWC), leaf area relative growth rate (RGRl) and leaf dry mass relative growth rate (RGRm) were the highest (76±2 %, 0.413 cm2 cm−2 d−1, 0.709 mg mg−1 d−1, respectively) at the beginning of the leaf expansion process (7 days after bud break). Leaf expansion lasted 84±2 days when
air temperature ranged from 13.3±0.8 to 27.6±0.9 °C. The net photosynthetic rate (P
N), stomatal conductance (g
s), and chlorophyll content per fresh mass (Chl) increased during leaf expansion, having the highest values [12.62±1.64 μmol
(CO2) m−2 s−1, 0.090 mol (H2O) m−2 s−1, and 1.03±0.08 mg g−1, respectively] 56 days after bud break. Chl was directly correlated with leaf dry mass (DM) and P
N. The thickness of palisade parenchyma contributed to the total leaf thickness (263.1±1.5 μm) by 47 %, spongy layer thickness
38 %, adaxial epidermis and cuticle thickness 9 %, and abaxial epidermis and cuticle thickness 6 %. Variation in leaf size
during leaf expansion might be attributed to a combination of cells density and length, and it is confirmed by the significant
(p<0.001) correlations among these traits. Q. ilex leaves reached 90 % of their definitive structure before the most severe drought period (beginning of June — end of August).
The high leaf mass area (LMA, 15.1±0.6 mg cm−2) at full leaf expansion was indicative of compact leaves (2028±100 cells mm−2). Air temperature increasing might shorten the favourable period for leaf expansion, thus changing the final amount of biomass
per unit leaf area of Q. ilex. 相似文献
5.
Gametophores of mosses Mnium undulatum and Polytrichum commune were submerged in distilled water or in calcium chloride solution (0.9 mM Ca2+) to induce hypoxia. The net photosynthetic (PN) and dark respiration rate (RD) were measured in the air containing 300–400 μmol(CO2)·mol−1(air) and 0.21 mol(O2)·mol−1(air). PN of M. undulatum gametophores decreased to 58 % of the control after 1-h submersion in water, whereas to 80 % of the control in P. commune gametophores. A smaller decrease in PN was observed when the gametophores were immersed in CaCl2 solution. In hypoxia, RD in the tested mosses species was a little higher than in the control. 相似文献
6.
This work aimed to evaluate if gas exchange and PSII photochemical activity in maize are affected by different irradiance
levels during short-term exposure to elevated CO2. For this purpose gas exchange and chlorophyll a fluorescence were measured on maize plants grown at ambient CO2 concentration (control CO2) and exposed for 4 h to short-term treatments at 800 μmol(CO2) mol−1 (high CO2) at a photosynthetic photon flux density (PPFD) of either 1,000 μmol m−2 s−1 (control light) or 1,900 μmol m−2 s−1 (high light). At control light, high-CO2 leaves showed a significant decrease of net photosynthetic rate (P
N) and a rise in the ratio of intercellular to ambient CO2 concentration (C
i/C
a) and water-use efficiency (WUE) compared to control CO2 leaves. No difference between CO2 concentrations for PSII effective photochemistry (ΦPSII), photochemical quenching (qp) and nonphotochemical quenching (NPQ) was detected. Under high light, high-CO2 leaves did not differ in P
N, C
i/C
a, ΦPSII and NPQ, but showed an increase of WUE. These results suggest that at control light photosynthetic apparatus is negatively
affected by high CO2 concentration in terms of carbon gain by limitations in photosynthetic dark reaction rather than in photochemistry. At high
light, the elevated CO2 concentration did not promote an increase of photosynthesis and photochemistry but only an improvement of water balance due
to increased WUE. 相似文献
7.
Photosynthetic Response of Carrots to Varying Irradiances 总被引:7,自引:3,他引:4
Response to irradiance of leaf net photosynthetic rates (P
N) of four carrot cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) were examined in a controlled
environment. Gas exchange measurements were conducted at photosynthetic active radiation (PAR) from 100 to 1 000 μmol m−2 s−1 at 20 °C and 350 μmol (CO2) mol−1(air). The values of P
N were fitted to a rectangular hyperbolic nonlinear regression model. P
N for all cultivars increased similarly with increasing PAR but Cascade and Oranza generally had higher P
N than CC. None of the cultivars reached saturation at 1 000 μmol m−2 s−1. The predicted P
N at saturation (P
Nmax) for Cascade, CC, Oranza, and RCC were 19.78, 16.40, 19.79, and 18.11 μmol (CO2) m−2 s−1, respectively. The compensation irradiance (I
c) occurred at 54 μmol m−2 s−1 for Cascade, 36 μmol m−2 s−1 for CC, 45 μmol m−2 s−1 for Oranza, and 25 μmol m−2 s−1 for RCC. The quantum yield among the cultivars ranged between 0.057–0.033 mol(CO2) mol−1(PAR) and did not differ. Dark respiration varied from 2.66 μmol m−2 s−1 for Cascade to 0.85 μmol m−2 s−1 for RCC. As P
N increased with PAR, intercellular CO2 decreased in a non-linear manner. Increasing PAR increased stomatal conductance and transpiration rate to a peak between
600 and 800 μmol m−2 s−1 followed by a steep decline resulting in sharp increases in water use efficiency.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
Diurnal and seasonal trends in net photosynthetic rate (P
N), stomatal conductance (g), transpiration rate (E), vapour pressure deficit, temperature, photosynthetic photon flux density, and water use efficiency (WUE) were compared
in a two-year-old Dalbergia sissoo and Hardwickia binata plantation. Mean daily maximum P
N in D. sissoo ranged from 21.40±2.60 μmol m−2 s−1 in rainy season I to 13.21±2.64 μmol m−2 s−1 in summer whereas in H. binata it was 20.04±1.20 μmol m−2 s−1 in summer and 13.64±0.16 μmol m−2 s−1 in winter. There was a linear relationship between daily maximum P
N and g
s in D. sissoo but there was no strong linear relationship between P
N and g
s in H. binata. In D. sissoo, the reduction in g
s led to a reduction in both P
N and E enabling the maintenance of WUE during dry season thereby managing unfavourable environmental conditions efficiently whereas
in H. binata, an increase in g
s causes an increase of P
N and E with a significant moderate WUE. 相似文献
9.
Seedlings of Bidens cernua L. emerged when mean air temperature was 17.0±1.3 °C. The highest net photosynthetic rate (P
N), 13.8±0.8 μmol(CO2) m−2 s−1, was monitored during the vegetative period (May–August), decreasing on an average by 50 % during flowering (August–September)
and during fruiting (September–November) phases. The senescence phase (October–November) was characterised by 79, 58, and
18 % decrease of P
N, chlorophyll content, and leaf area (LA), respectively, from the maximum values. The time span from seedling emergence to
the end of fruiting phase was 202 d. The total plant biomass was 1.58±0.05 g of which 81 % was aboveground plant portion.
The total dry mass relative growth rate averaged over the assimilation period was 0.0804±0.0002 kg kg−1 d−1, and it was correlated to both the net assimilation rate (NAR) and the leaf area ratio (LAR). 相似文献
10.
Differences in leaf traits among the dune species developing along the Latium coast were analysed. Cakile maritima Scop. subsp. maritima, Elymus farctus (Viv.) Runemark ex Melderis subsp. farctus, Ammophila arenaria (L.) Link subsp. australis (Mabille) Lainz, Ononis variegata L., Pancratium maritimum L., Eryngium maritimum L., and Anthemis maritima L. were considered. The considered species showed a similar net photosynthetic rate (P
N) and chlorophyll content (Chl) during the year, with a peak from the end of April to the middle of May [13.0±3.6 μmol (CO2) m−2 s−1 and 0.63±0.21 mg g−1, respectively, mean values of the considered species], favoured by air temperature in the range 13.3–17.5°C, and 6% of soil
water availability. In June–July, the increase of air temperature (Tmax = 28.4°C), associated with a lower water availability (42 mm, total rainfall of the period) and a 1% of soil water availability
determined a significant decrease of P
N (59%, mean of the considered species) and Chl (38%), and an increase of the carotenoid (Car)/Chl ratio (59%). The significant
correlation between P
N and stomatal conductance (g
s) (p<0.05) explained 67% of P
N variations. Moreover, the correlation between P
N and leaf temperature (T
l) underlined that the favourable T
l enabling 90–100% of the highest P
N for the considered species was within the range 23.4 to 26.6°C. P
N decreased below half of its maximum value when T
l was over 35.8 and 37.4°C for E. farctus subsp. farctus and A. arenaria subsp. australis, respectively and over 32.2°C for the other considered species (mean value). Leaf mass area (LMA) varied from 6.8 ± 0.7 mg
cm−2 (O. variegata) to 30.6 ± 1.6 mg cm−2 (A. arenaria). PCA (principal component analysis) carried out using the considered morphological and physiological leaf traits underlined
that the co-occurring species were characterised by different adaptive strategies: E. farctus and A. arenaria photosynthesized for a long period also when air temperature was over 35.8 and 37.4°C, respectively, because of their lower
transpiration rates [E, 1.4 ± 0.1 mmol (H2O) m−2 s−1], which seemed to be controlled by the highest LMA. On the contrary, A. maritima and C. maritima subsp. maritima had a higher P
N (on an average 52% higher than the others) in the favourable period, allowed by the highest succulence index (SI, 85.7 ±
9 mg cm−2) and the lower LMA. The results allowed us to hypothesize that A. arenaria and E. farctus might be at a competitive advantage relative to the other considered species with respect to the increase of air temperature,
by their ability to photosynthesize at sufficient rates also during summer. 相似文献
11.
A controlled growth chamber experiment was conducted to investigate the short-term water use and photosynthetic responses
of 30-d-old carrot seedlings to the combined effects of CO2 concentration (50–1 050 μmol mol−1) and moisture deficits (−5, −30, −55, and −70 kPa). The photosynthetic response data was fitted to a non-rectangular hyperbola
model. The estimated parameters were compared for effects of moisture deficit and elevated CO2 concentration (EC). The carboxylation efficiency (α) increased in response to mild moisture stress (−30 kPa) under EC when
compared to the unstressed control. However, moderate (−55 kPa) and extreme (−70 kPa) moisture deficits reduced α under EC.
Maximum net photosynthetic rate (P
Nmax) did not differ between mild water deficit and unstressed controls under EC. Moderate and extreme moisture deficits reduced
P
Nmax by nearly 85 % compared to controls. Dark respiration rate (R
D) showed no consistent response to moisture deficit. The CO2 compensation concentration (Γ) was 324 μmol mol−1 for −75 kPa and ranged 63–93 μmol mol−1 for other moisture regimes. Interaction between moisture deficit and EC was noticed for P
N, ratio of intercellular and ambient CO2 concentration (C
i/C
a), stomatal conductance (g
s
), and transpiration rate (E). P
N was maximum and C
i/C
a was minimum at −30 kPa moisture deficit and at C
a of 350 μmol mol−1. The g
s and E showed an inverse relationship at all moisture deficit regimes and EC. Water use efficiency (WUE) increased with moisture
deficit up to −55 kPa and declined thereafter. EC showed a positive influence towards sustaining P
N and increasing WUE only under mild moisture stress, and no beneficial effects of EC were noticed at moderate or extreme moisture
deficits. 相似文献
12.
Using CO2 gasometry, net photosynthetic (P
N) and dark respiration rates (R
D) were measured in leaves or traps of 12 terrestrial carnivorous plant species usually grown in the shade. Generally, mean
maximum P
N (60 nmol CO2 g−1(DM) s−1 or 2.7 μmol m−2 s−1) was low in comparison with that of vascular non-carnivorous plants but was slightly higher than that reported elsewhere
for carnivorous plants. After light saturation, the facultatively heliophytic plants behaved as shade-adapted plants. Mean
R
D in leaves and traps of all species reached about 50% of maximum P
N and represents the high photosynthetic (metabolic) cost of carnivory. 相似文献
13.
The relationship between net photosynthetic (P
N) and leaf respiration (R) rates of Quercus ilex, Phillyrea latifolia, Myrtus communis, Arbutus unedo, and Cistus incanus was monitored in the period February 2006 to February 2007. The species investigated had low R and P
N during winter, increasing from March to May, when mean air temperature reached 19.2 °C. During the favourable period, C. incanus and A. unedo had a higher mean P
N (16.4±2.4 μmol m−2 s−1) than P. latifolia, Q. ilex, and M. communis (10.0±1.3 μmol m−2 s−1). The highest R (1.89±0.30 μmol m−2 s−1, mean of the species), associated to a significant P
N decrease (62 % of the maximum, mean value of the species), was measured in July (mean R/P
N ratio 0.447±0.091). Q10, indicating the respiration sensitivity to short-term temperature increase, was in the range 1.49 to 2.21. Global change
might modify R/P
N determining differences in dry matter accumulation among the species, and Q. ilex and P. latifolia might be the most favoured species by their ability to maintain sufficiently higher P
N and lower R during stress periods. 相似文献
14.
M. Moynul Haque A. Hamid M. Khanam D. K. Biswas M. A. Karim Q. A. Khaliq M. A. Hossain D. C. Uprety 《Biologia Plantarum》2006,50(1):69-73
The effect of elevated CO2 concentration (CE) on leaf chlorophyll (Chl) and nitrogen (N) contents and photosynthetic rate (PN) was evaluated during the post-flowering stages of rice grown at CE (570 ± 50 μmol mol−1) in open top chamber (OTC), at ambient CO2 concentration (∼ 365 μmol mol−1) in OTC and at open field. Thirty-five day old seedlings were transplanted in OTCs or in field and allowed to grow till maturity.
Chl and N contents were highest at the time of flowering and thereafter it started to decline. The rate of decline in Chl
and N contents was faster in plants grown under CE mostly in later part of growth. Irrespective of treatment difference, flag
leaf contained the highest amount of Chl and N than penultimate and third leaf. The higher PN was observed in leaves under CE than in the leaves in other two growing conditions. Considering growth stage, PN was the highest at flowering which reduced at the later part of growth due to degradation of Chl and N content of the leaf.
Under CE it was 40.02 μmol m−2 s−1 at flowering and it reduced to only 14.77 μmol m−2 s−1 at maturity stage. The beneficial effect of CE in increasing leaf PN may be maintained by applying extra dose of nitrogen at the later stages of plant growth. 相似文献
15.
The differences in pigment levels, photosynthetic activity and the chlorophyll fluorescence decrease ratio R
Fd (as indicator of photosynthetic rates) of green sun and shade leaves of three broadleaf trees (Platanus acerifolia Willd., Populus alba L., Tilia cordata Mill.) were compared. Sun leaves were characterized by higher levels of total chlorophylls a + b and total carotenoids x + c as well as higher values for the weight ratio chlorophyll (Chl) a/b (sun leaves 3.23–3.45; shade leaves: 2.74–2.81), and lower values for the ratio chlorophylls to carotenoids (a + b)/(x + c) (with 4.44–4.70 in sun leaves and 5.04–5.72 in shade leaves). Sun leaves exhibited higher photosynthetic rates P
N on a leaf area basis (mean of 9.1–10.1 μmol CO2 m−2 s−1) and Chl basis, which correlated well with the higher values of stomatal conductance G
s (range 105–180 mmol m−2 s−1), as compared to shade leaves (G
s range 25–77 mmol m−2 s−1; P
N: 3.2–3.7 μmol CO2 m−2 s−1). The higher photosynthetic rates could also be detected via imaging the Chl fluorescence decrease ratio R
Fd, which possessed higher values in sun leaves (2.8–3.0) as compared to shade leaves (1.4–1.8). In addition, via R
Fd images it was shown that the photosynthetic activity of the leaves of all trees exhibits a large heterogeneity across the
leaf area, and in general to a higher extent in sun leaves than in shade leaves. 相似文献
16.
Chlorophyll (Chl) content, dry mass, relative water content (RWC), leaf mass per area (LMA), proline (Pro) content, malondialdehyde
(MDA) content, superoxide dismutase (SOD) and peroxidase (POD) activity, P
N-PAR response curves and gas exchange were studied to determine the effects of water stress on photosynthetic activity, dry
mass partitioning and metabolic changes in four provenances of neem (Azadirachta indica A. Juss). The results indicated that provenance differences existed in the adaptation response to water stress that included
changes to growth strategies coupled with ecophysiological and metabolic adjustments. As water stress increased, stomatal
conductance (g
s), net photosynthetic rate (P
N), transpiration rate (E), and leaf RWC decreased while LMA increased in all provenances. Dry mass was reduced in droughted plants and the percentage
increased in dry mass allocated to roots, and enzyme activities of SOD and POD were highest in neem originating from Kalyani
(KA) provenance and lowest in neem originating from New Dehli (ND) provenance. In contrast, water stress increased MDA content
least in KA and most in ND. Furthermore, neem originating from ND also had the greatest decrease in Chl a/b ratio while the ratio was least affected in neem originating from KA. These findings suggest neem originating from KA may
have more drought resistance than neem originating from ND. The data from P
N-PAR response curves are less clear. While these curves showed that drought stress increased compensation irradiance (I
c) and dark respiration (R
D) and decreased saturation irradiance (I
s) and maximum net photosynthetic rate (P
max), the extent of decline in P
max was provenance dependent. P
max under non-waterlimiting conditions was higher in neem originating from Jodhpur (MA) (about 14 μmol m−2 s−1) than in the other three provenances (all about 10 μmol m−2 s−1), but mild water stress had minimal effect on P
max of these three provenances whereas P
max of MA provenance declined to 10 μmol m−2 s−1, i.e. a similar value. However, under severe water stress P
max of MA and KA provenances had declined to 40% of non-stressed values (about 6 and 4 μmol m−2 s−1, respectively) whereas the decline in P
max of neem originating from Kulapachta (KU) and ND provenances was about 50% of nonstressed values (about 5 μmol m−2 s−1). These data suggest the P
N responses of KU and ND provenances are most tolerant, and KA and MA least tolerant to increasing water stress, but also suggest
MA provenance could be the most desired under both non-water-limiting and water-limiting conditions due to highest P
max in all conditions. 相似文献
17.
We determined the interactive effects of irradiance, elevated CO2 concentration (EC), and temperature in carrot (Daucus carota var. sativus). Plants of the cv. Red Core Chantenay (RCC) were grown in a controlled environmental plant growth room and exposed to 3
levels of photosynthetically active radiation (PAR) (400, 800, 1 200 μmol m−2 s−1), 3 leaf chamber temperatures (15, 20, 30 °C), and 2 external CO2 concentrations (C
a), AC and EC (350 and 750 μmol mol−1, respectively). Rates of net photosynthesis (P
N) and transpiration (E) and stomatal conductance (g
s
) were measured, along with water use efficiency (WUE) and ratio of internal and external CO2 concentrations (C
i/C
a). P
N revealed an interactive effect between PAR and C
a. As PAR increased so did P
N under both C
a regimes. The g
s
showed no interactive effects between the three parameters but had singular effects of temperature and PAR. E was strongly influenced by the combination of PAR and temperature. WUE was interactively affected by all three parameters.
Maximum WUE occurred at 15 °C and 1 200 μmol m−2 s− 1 PAR under EC. The C
i
/C
a
was influenced independently by temperature and C
a. Hence photosynthetic responses are interactively affected by changes in irradiance, external CO2 concentration, and temperature. EC significantly compensates the inhibitory effects of high temperature and irradiance on
P
N and WUE. 相似文献
18.
The use of Jatropha curcas oil as a source of biofuel has been well-explored. However, the physiological and growth studies of J. curcas have received considerably lesser attention. In this study, leaf gas exchange measurements and leaf nitrogen content were
determined for four varieties of J. curcas, grown in the field or in pots. Based on stable carbon isotope analysis (δ13C) and gas-exchange studies, J. curcas is a C3 sun plant and the range of leaf photosynthetic rates (or CO2 assimilation rates, P
Nmax) were typically between 7 and 25 μmol(CO2) m−2 s−1 and light saturation generally occurred beyond 800 μmol(quanta) m−2 s−1. Higher rates of leaf photosynthesis were generally obtained with the mature leaves. In addition, increased foliar P
Nmax were recorded in potted J. curcas variety Indiana with increasing nitrogen (N) nutrition levels. These plants also showed greater growth, increased leaf N
content, higher maximum CO2 assimilation capacity (P
NhighCO2) and chlorophyll (Chl) content, indicating the potential of optimizing the growth of Jatropha by varying fertilizer nutrient levels. A rapid assessment for leaf N using a nondestructive and portable Chl meter had been
established for J. curcas. This approach will allow repeated sampling of the same plant over time and thus enable the monitoring of the appropriate
levels of soil fertility to achieve good Jatropha plantation productivity. High N nutrition improved the overall plant oil yield by increasing the total number of fruits/seeds
produced per plant, while not affecting the intrinsic seed oil content. 相似文献
19.
In carob tree (Ceratonia siliqua) radiant energy saturated net photosynthetic rate (P
N) during summer was about 10 % of the spring values. This was accompanied by a reduction in stomatal conductance (g
s), which only partially explains the strong reduction in P
N. Photosynthetic capacity (P
max) and quantum yield (Φ), both measured under saturating CO2, had the maximum in spring (about 34 μmol m−2 s−1 and 0.08 mol mol−1, respectively) and both decreased in late summer to about 55 % of their spring values. Despite strong decreases in Φ, photoinhibition
of photosystem 2 (PS2) was negligible or easily reversible in carob leaves subjected to summer drought, since Fv/Fm, measured in the morning, did not show appreciable changes. The recovery of affected parameters was very rapid after the
first rains in late October. The chlorophyll (Chl) alb ratio in the end of the summer was 2.6, a value significantly lower than 3.6 obtained in the spring, suggesting that Chl
a was preferentially reduced.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
N2O, CH4 and CO2 emissions from seasonal tropical rainforests and a rubber plantation in Southwest China 总被引:2,自引:1,他引:1
Christian Werner Xunhua Zheng Janwei Tang Baohua Xie Chunyan Liu Ralf Kiese Klaus Butterbach-Bahl 《Plant and Soil》2006,289(1-2):335-353
The main focus of this study was to evaluate the effects of soil moisture and temperature on temporal variation of N2O, CO2 and CH4 soil-atmosphere exchange at a primary seasonal tropical rainforest (PF) site in Southwest China and to compare these fluxes with fluxes from a secondary forest (SF) and a rubber plantation (RP) site. Agroforestry systems, such as rubber plantations, are increasingly replacing primary and secondary forest systems in tropical Southwest China and thus effect the N2O emission in these regions on a landscape level. The mean N2O emission at site PF was 6.0 ± 0.1 SE μg N m−2 h−1. Fluxes of N2O increased from <5 μg N m−2 h−1 during dry season conditions to up to 24.5 μg N m−2 h−1 with re-wetting of the soil by the onset of first rainfall events. Comparable fluxes of N2O were measured in the SF and RP sites, where mean N2O emissions were 7.3 ± 0.7 SE μg N m−2 h−1 and 4.1 ± 0.5 SE μg N m−2 h−1, respectively. The dependency of N2O fluxes on soil moisture levels was demonstrated in a watering experiment, however, artificial rainfall only influenced the timing of N2O emission peaks, not the total amount of N2O emitted. For all sites, significant positive correlations existed between N2O emissions and both soil moisture and soil temperature. Mean CH4 uptake rates were highest at the PF site (−29.5 ± 0.3 SE μg C m−2 h−1), slightly lower at the SF site (−25.6 ± 1.3 SE μg C m−2 h−1) and lowest for the RP site (−5.7 ± 0.5 SE μg C m−2 h−1). At all sites, CH4 uptake rates were negatively correlated with soil moisture, which was also reflected in the lower uptake rates measured in the watering experiment. In contrast to N2O emissions, CH4 uptake did not significantly correlate with soil temperature at the SF and RP sites, and only weakly correlated at the PF site. Over the 2 month measurement period, CO2 emissions at the PF site increased significantly from 50 mg C m−2 h−1 up to 100 mg C m−2 h−1 (mean value 68.8 ± 0.8 SE mg C m−2 h−1), whereas CO2 emissions at the SF and RP site where quite stable and varied only slightly around mean values of 38.0 ± 1.8 SE mg C m−2 h−1 (SF) and 34.9 ± 1.1 SE mg C m−2 h−1 (RP). A dependency of soil CO2 emissions on changes in soil water content could be demonstrated for all sites, thus, the watering experiment revealed significantly higher CO2 emissions as compared to control chambers. Correlation of CO2 emissions with soil temperature was significant at the PF site, but weak at the SF and not evident at the RP site. Even though we demonstrated that N and C trace gas fluxes significantly varied on subdaily and daily scales, weekly measurements would be sufficient if only the sink/ source strength of non-managed tropical forest sites needs to be identified. 相似文献