Growth and ecophysiological characterisation of the bamboo Phyllostachys humilis Muroi in a plantation in Ireland.

摘要

In the 21st century people all over the world are confronted with the search to reduce greenhouse gas emissions and to enhance the production of renewable energy and bio-based products. Bamboo --- as one of the fastest growing plant species -- can contribute to this bio-based economy since it has many uses in this field. The plant is native to Asia, Africa and South America, and is broadly represented, with tropical and temperate species. Although non native to Europe, numerous bamboo species are growing well in European gardens. However, this does not necessarily imply that bamboo should be introduced as a field crop for biomass production on this continent. In this thesis, the aim is therefore to investigate and describe the growth potential and characteristics of a temperate bamboo species on a test field in Ireland. Based on the biomass yields of two harvests of this test field, Phyllostachys humilis turned out to be the best candidate of five different Phyllostachys spp. to be studied in detail.;In a first part of the study, heliometric relations were determined, and a linear relation between length and width of the leaves and leaf area was established, as well as a linear relation between the square root of the fresh calm weight and the product of length and average mean diameter of the calm. This relation enables us to estimate future yields without harvesting standing biomass. Furthermore, a seasonal variation in biomass distribution was found, with relatively more leaf material in summer compared to spring and autumn, resulting in higher relative water content when total biomass would be harvested in summer compared to a harvest in the other seasons. Also, a vertical variation in the plant canopy was found when determining the specific leaf area (SLA). SLA was significantly lower in the top leaves than in the leaves at the base of the plant, probably related to the relative high leaf area index (LAI) of the bamboo canopy, and to the absorption of incident solar radiation by such dense canopies related to high LAI values. The LAI showed no seasonal variation and the LAI of the bamboo canopy was found to be 7 m 2leafm-2soil, which is comparable with literature values for bamboo canopies in native regions.;Since we were interested in the performance of the bamboo leaves, chlorophyll fluorescence was measured to study the effect of the environmental conditions on the photochemical efficiency of the leaves. The chlorophyll fluorescence showed a seasonal variation, with a lower photochemical efficiency during spring, compared to the rest of the year. During this spring season, also minor diurnal variations were observed, with a different photochemical efficiency in the morning compared to the noon and afternoon. These variations should be taken into account in future measurements. For unambiguous measurements, it is therefore advised to measure at a fixed time during noon or afternoon. Also a vertical (in-depth canopy) variation was observed, and this in all seasons: photochemical efficiency in the top leaves was lower compared to the leaves at the base of the plant.;To explain these time- and space-related variations in photochemical efficiency, a growth chamber experiment was set up to see if these variations are possibly linked with environmental conditions. We found that the combination of low air temperature and relative high light intensities lowers the performance of the plants photosynthetic system, as was most likely the case in the spring season in Ireland. Therefore, we hypothesized that the vertical variations observed in the bamboo plantation in the field can be ascribed to the different environmental conditions between sun-exposed top leaves and the more protected/covered leaves at the base.;Photochemical efficiency and photosynthetic rates are frequently correlated, although their relation is not unambiguous. Therefore, we studied the seasonal, diurnal and vertical (in-canopy) variation of the different photosynthetic parameters in the bamboo plantation. We determined the photosynthetic parameters of two frequently used photosynthesis models, namely the empirical light response curve (LRC) model and the biochemical Farquhar, Von Caemmerer and Berry (FvCB) model. For both approaches, neither diurnal nor vertical variations were found. Remarkably, the difference between top leaves and leaves at the base of the plant, as expressed by the SLA and photochemical efficiency, is not reflected in the photosynthetic parameters of the two above mentioned models. Nevertheless, a seasonal variation was found, with high photosynthetic rates in autumn and low photosynthetic rates in spring, which is in accordance to the observations of the photochemical efficiency in these seasons. Low photosynthetic rates can also be related to high sugar or starch contents in the leaves, as these can inhibit photosynthesis by a feedback mechanism. For this reason, and also to estimate the quality of harvested bamboo, free glucose content and starch content was determined for bamboo leaves, lateral branches and culms for the different seasons. High sugar contents during the winter period probably serve as a protection mechanism against frost damage. The subsequent increase of starch during early spring might decrease photosynthetic rates during spring. Furthermore, compared to the leaves, a higher starch content was present in the woody tissues, whereas free glucose content was higher in the leaves, which is in agreement with the flow pressure hypothesis of Munch.;In general, many characteristics of the bamboo plants show a seasonal variation, with autumn seems to be the season in which the plant is fully matured and has the highest potential photosynthetic rates. Some plant parameters such as chlorophyll fluorescence also show diurnal and vertical variations. These latter are most likely caused by the relative high density of the bamboo canopy. These variations should be taken into account when modelling bamboo growth. Based on all observations, bamboo is able to grow in Europe with yields of 5-8 t ha-1 y-1 in Ireland, which are competitive values to e.g. Miscanthus spp., another crop typically used for biomass production, producing 3-5 t ha-1 y-1 in Ireland. The plant characteristics determined in this study are making it possible to develop a growth model, to determine biomass yields in Europe and elsewhere. However, the SWOT-analysis of bamboo as a crop in Europe shows strengths as well as weaknesses, and this, together with the different opportunities and threats, still renders the future for bamboo production in Europe rather ambiguous.