Elevated CO2 does not increase eucalypt forest productivity on a low-phosphorus soil
Summary (1 min read)
Methods
- Methods, including statements of data availability and any associated references, are available in the online version of this paper.
- Diameter class (cm) These effects are shown for leaf net photosynthesis (a, left side) and aboveground net primary production, ANPP from 2013 to 2015 (b, right side).
- The mixed-model repeated-measures analysis for photosynthesis was done using data shown in Fig. 1a ), with the time term indicating sampling date across three years.
- For ANPP, the time term is 'year', the first to third year of the full eCO2 treatment.
- In both analyses, a mixed-model repeated-measures analysis was done using a fixed treatment (CO2) and a random plot effect, and Type III sums of squares computed using restricted maximum likelihood estimates for F-tests.
Methods (online)
- Six large circular plots (0.05 ha each) were established in 2010 in a mature eucalypt woodland on an alluvial spodosol in western Sydney, Australia.
- The location receives 800 mm of precipitation per annum on average and has a mean annual temperature of 17.5°C (www.bom.gov.au).
- For the leaf component, the productivity was computed as the sum of annual litterfall whilst for twigs the authors assume strictly annual turnover across the three years.
- The authors analysed the photosynthesis data 35 using a mixed-model repeatedmeasures analysis of variance in R v3.3.1 using the 'lme4' function within the 'nlme' package, with CO2 treatment as a fixed factor and plot as a random factor nested within CO2 treatment.
- All data were checked for normality using the Q-Q plots and Levene's test, and residuals from model fitting were checked for evidence of heteroscedasticity.
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Frequently Asked Questions (14)
Q2. How was the CO2 effect size calculated?
379 Confidence intervals for the CO2 effect size estimate were computed in R (http://cran.r-380 project.org) using the function ‘confint’, which applies quantile functions for the t-381 distribution after model-fitting.
Q3. How many trees were measured across the ambient and elevated plots?
Of a total of 146 trees measured across the ambient and 353 elevated plots, 49 suppressed trees, 6 co-dominant trees with trunk defects, and 4 trees 354 showing shrinkage possibly preceding mortality were omitted from the mixed-model 355 analysis.
Q4. What is the mean of the ANPP in a mature Eucalyptus?
Stemwood 281 production is determined as the annual biomass increment, and foliage+fine twig production 282 are measured as annual biomass turnover collected monthly in permanent litter baskets.
Q5. What was the productivity of the leaf 367 component?
For the leaf 367 component, the productivity was computed as the sum of annual litterfall whilst for twigs the authors 368 assume strictly annual turnover across the three years.
Q6. What is the mean temperature in the warmest month?
Mean maximum temperature in the warmest month is 30°C and mean 319 minimum temperature in the coldest month is 3.6°C, with monthly mean temperatures always 320 > 10°C.
Q7. What was the effect of the CO2 on the tree crown?
A smaller set of 339measurements on shaded foliage within the tree crowns was used to confirm results from the 340 upper-crown measurements in terms of the CO2-enhancement effect on photosynthesis, thus 341 the entire crown can be expected to behave similarly.
Q8. How was the data checked for normality?
All data were checked for normality 386 using the Q-Q plots and Levene’s test, and residuals from model fitting were checked for 387 evidence of heteroscedasticity.
Q9. What is the mean response ratio for photosynthesis in a mature Eucalyptus?
The CO2 fertilisation response ratio for photosynthesis over time, 268 with grey areas representing two-sided 95% confidence intervals for the CO2 fertilisation 269 response ratio for each of the measurement timepoints.
Q10. What is the ANPP of the Eucalyptus?
Total ANPP is represented by the 279 combination of stemwood biomass production (stippled), fine twig and bark production 280(striped), seed and capsule production (hatched), and leaf production (solid).
Q11. How long did the eCO2 study last?
The P-addition treatments were 331 maintained through the duration of the study, resulting in 4 years of P-fertilisation concurrent 332 with the 3-year eCO2 study.
Q12. How was the diameter of each tree measured?
The diameter 345 of each tree was measured at 1.3 m height at approximately monthly intervals starting 346 February 2011, 2 years prior to commencement of the full CO2 treatment.
Q13. How many trees were measured across all years?
The authors thus used a total of N=87 trees measured across all years and without stem 356 defects, suppression or shrinkage in the mixed-model analyses.
Q14. how many datasets are available in a research data australia repository?
The datasets generated during and/or analysed during the current study are 390 available in a Research Data Australia repository (http://doi.org/10.4225/35/57ec5d4a2b78e).