Mark Bloomberg

Hydrothermal time germination models for radiata pine (Pinus radiata D. Don)

The objective of this study was to fit a hydrothermal germination model to germination data for a seedlot of radiata pine (Pinus radiata D. Don). Seeds were incubated for 50 d at constant temperatures and water potentials (T ¼ 12.5‐32.58C, C ¼ 0t o21.2 MPa). Most seeds completed germination within 50 d, but for low C and/or non-optimal temperatures (T , 17.58C, T . 258C) many seeds did not complete germination. In general, germination data conformed to the hydrothermal model. Departures from the model were encountered for slow-germinating seeds at suboptimal temperatures (T # 208C). To account for these departures, two alternative hydrothermal models were fitted with an additional term for an upwards shift in seed base water potential with increasing time to germination. The alternative models more correctly predicted germination time than the original model. Similarly, reduced percentage germination at supra-optimal temperatures (T . 208C) was explained by including a term in the hydrothermal model which shifted the base water potential of seeds upwards towards zero, which in turn reduced the predicted rate that hydrothermal time would be accumulated by seeds. The rate of this upwards shift in base water potential was dependent on time to complete germination and ambient water potential as well as supra-optimal temperature.

Modelling seed germination in response to continuous variables: use and limitations of probit analysis and alternative approaches

Probit-based models relating a proportional response variable to a temporal explanatory variable, assuming that the times to response are normally distributed within the population, have been used in seed biology for describing the rate of loss of viability during seed ageing and the progress of germination over time in response to environmental signals (e.g. water, temperature). These models may be expressed as generalized linear models (GLMs) with a probit (cumulative normal distribution) link function, and, using GLM fitting procedures in current statistical software, parameters of these models are efficiently estimated while taking into account the binomial error distribution of the dependent variable. The fitted parameters can then be used to calculate the ‘traditional’ model parameters, such as the hydro- or hydrothermal time constant, the mean or median response of the seeds (e.g. mean time to death, median base water potential), and the standard deviation of the normal distribution of that response. Furthermore, through consideration of the deviance and residuals, performing model evaluation and modification can lead to improved understanding of the underlying physiological/ecological processes. However, fitting a binomial GLM is not appropriate for the cumulative count data often collected from germination studies, as successive observations are not independent, and time-to-event/survival analysis should be considered instead. This review discusses well-known probit-based models, providing advice on how to collect appropriate data and fit the models to those data, and gives an overview of alternative analysis approaches to improve understanding of the underlying mechanisms of seed dormancy and germination behaviour.

The effects of subsurface irrigation at different soil water potential thresholds on the growth and transpiration of Populus tomentosa in the North China Plain

Summary In order to find the optimal subsurface drip irrigation (SDI) scheduling for mature triploid Populus tomentosa plantations in the North China Plain, a field experiment was conducted in 2010 and 2011 to investigate the effects of SDI at different soil water potential (SWP) thresholds on the growth and transpiration of a P. tomentosa plantation when it was six and seven years old. The experiment included three SWP treatments, which initiated irrigation when the SWP at 20 cm depth and 10 cm distance from a drip emitter reached −25 (T25), −50 (T50) and −75 (T75) kPa, respectively. A control non-irrigation treatment (CK) was also included. Long-term SWP, soil water content (SWC), transpiration, tree growth, meteorological factors and groundwater level were monitored. Results showed that SDI influenced the SWC only in 0–80 cm of soil. From April to July, on average, the cumulative stand-level transpiration on a ground area basis (E) and growth of basal area at breast height accounted for 81% and 93% of their corresponding whole-season values, while the cumulative reference crop potential evapotranspiration (ET0) was 43% higher than the rainfall. In contrast, from August to October, the growth rate of P. tomentosa was very slow, while the cumulative rainfall was 36% higher than ET0 and the average groundwater level was relatively high (125 cm). Relative to CK, the E under the SWP treatments was significantly (P < 0.05) increased by 20–73%. Decreasing the SWP irrigation threshold from −25 to −50 kPa significantly reduced E by 31% (P < 0.05), but decreasing the threshold from −50 to −75 kPa did not further reduce P. tomentosa E. Relative to CK, T25, T50 and T75 increased the annual above-ground dry biomass (ADB) increment by 54% (P < 0.05), 34% (P < 0.05) and 24% (P > 0.05) in 2010, and by 28% (P > 0.05), 29% (P > 0.05) and 32% (P < 0.05) in 2011, respectively. However, no significant difference in ADB increment was detected among the SWP treatments. Based on these results, it can be concluded that when planting P. tomentosa at sites with similar characteristics to ours in the North China Plain: (1) SDI could be promoted in the cultivation of P. tomentosa to improve tree growth; (2) a range of −50 to −75 kPa at a depth of 20 cm and 10 cm distant from a drip emitter is recommended as the irrigation threshold for scheduling SDI in P. tomentosa plantations and (3) irrigation should be applied between April and July, while drainage should be implemented between August and October.

Combined effects of cotyledon excision and nursery fertilization on root growth, nutrient status and outplanting performance of Quercus variabilis container seedlings

Artificial excision of the distal part of acorns in order to promote germination is well researched in oak seedling cultivation studies. However, studies of combined effects of cotyledon excision and nursery fertilization on container seedlings are lacking, especially for seedling root growth and outplanting performance. This study aimed to explore the main effects of cotyledon excision on Quercus variabilis seedling emergence characteristics and demonstrated the combined effects of cotyledon excision and nursery fertilization on seedling quality to improve Quercus variabilis seedling outplanting performance. Four cotyledon excision treatments and two classes of nursery fertilization were implemented. Seedling emergence was noted every week after sowing. Seedling dry mass, morphology, and nutrient status were assessed at the end of the nursery season. After the first outplanting season, the aforementioned measurements along with seedling survival were determined once again. The results showed that cotyledon excision generally induced greater and more rapid seedling emergence, but did not affect shoot emergence synchronicity. The highest total emergence and emergence rate occurred with Intermediate excision (1/2 of the distal end of acorn was excised). Effects of nutrient loss due to cotyledon excision on seedling quality and outplanting performance were somewhat compensated by nursery fertilization. Nursery fertilization promoted dry mass increment (the net increment from T0 to T2 for dry mass) for excised seedlings after outplanting, resulting in better performance for Slight (1/3 of the distal end of acorn was excised) and Intermediate excision treatments in the field. Thus we conclude Intermediate excision combined with reasonable nursery fertilization can be recommended for production of nursery grown seedlings for afforestation.

Indolebutryic acid and wounding induced rooting in callused, non‐rooted Leyland cypress (× Cupressocyparis leylandii) stem cuttings

Abstract Callused, non‐rooted Leyland cypress (× Cupressocyparis leylandii) stem cuttings were treated with different wounding treatments (no, single and double wound) and solutions of indolebutyric acid (IBA) (0,5000, and 10 000 ppm). Double wound and 10 000 ppm IBA resulted in the highest percentage of rooted cuttings compared with all other treatments. Wounding had no effect on the number of primary roots produced per rooted cutting, however, cuttings treated with 10 000 ppm IBA formed significantly more roots than non‐treated cuttings (4.5 and 2.6, respectively).

Developing a framework for growth modelling in a managed southern black beech forest

BackgroundA model of individual tree growth using simple predictors in a managed black beech (Fuscospora solandri (Hook.f.) Heenan & Smissen) forest could provide a useful tool for predicting future stand characteristics.MethodsData from permanent sample plots were used to develop a framework for modelling individual tree growth in Woodside forest, a managed black beech forest in north Canterbury (New Zealand). We tested three mixed-effect models to identify effects of sites, treatment (thinnings), individual tree size and competition on tree growth rates.ResultsA power function amended with variables specifying stand basal area and thinning treatment was best suited for black beech, explaining about 55% of the variation in growth rates. Treatment history (thinnings), as well as the individual tree size and the stand basal area, strongly affected tree diameter growth. Only 3% of the variation in diameter growth rates was explained by plot-specific effect which was less than observed in earlier studies.ConclusionsAll predictor variables (management history, individual tree diameter and stand basal area) are quite simple to measure in the field and could be easily used to predict diameter increments in managed or unmanaged forests. A limitation of our study was that available growth data in Woodside were from small plots, focused on a small number of trees and a narrow range of diameters. However, our results are a good starting point, providing a promising framework for further modelling of tree growth in Woodside forest from new permanent plot data.

Assessment of the accuracy of profile available water and potential rooting depth estimates held within New Zealand

The Fundamental Soil Layers (FSL) serve historically as New Zealand’s primary source of soil information. They contain a range of New Zealand’s soil attribute information held in a spatial database. Despite their wide use in a range of applications, few direct assessments of the accuracy of FSL attribute information have been undertaken to date. This study aims to provide an assessment of the accuracy of the FSL by comparing observed data for Profile Available Water (PAW) and Potential Rooting Depth (PRD) with FSL estimates for these two attributes. Two datasets were used to conduct the tests. The first dataset (n = 35) contained measured observations for PAW and PRD. A second dataset (n = 173) contained measured observations for PRD only. A regression model found a weak relationship between measured values and FSL estimates for PAW and PRD (correlations ranged from –0.08 to 0.17). Additional FSL estimates provided in the form of class intervals were tested by calculating the proportion of observed values within the specified FSL class interval. The effect of estimate lineage (underlying data and estimation method) on the accuracy of the class intervals was assessed using a logistic regression. Overall the FSL estimates for PRD and PAW were inaccurate, and allowance for data lineage did not improve the accuracy of the FSL estimates.