2.2 Cultivation and harvest
To avoid root damage from transplanting and to improve seedling
survival, we established monocultures by sowing the seeds and then
thinning the seedlings. Before sowing, the surface of the planting pots
was evenly gridded using yarn according to the number of seeds to be
sown. All the seeds were sterilized with 75% alcohol solution for 10
minutes and then washed with distilled water three times. Then, the
seeds were placed into the corresponding grid to a depth of
approximately 1 cm from the surface of the substrate. A backup pot was
prepared for each species, and seedlings were replanted if they died
within two weeks after thinning (Figure S1). The average day/night
temperature in the greenhouse was 28.5/18.5 °C, and the relative
humidity was between 40% and 60%. The positions of the pots were
randomly changed within and between blocks every two weeks. Each pot was
watered with a measured amount every 3 to 5 days to ensure plant growth.
In the middle and late cultivation stages, we raised the planting pots
with nylon netting to prevent ‘competition escape’ of aboveground organs
and to make the conditions as similar to field conditions as possible
(Figure S2).
The experiment was conducted from August 19, 2019, to January 12, 2020.
As the annuals (C. glaucum and S. viridis ) had relatively
short life spans, they were harvested in the eighth week. Before
harvesting, each plant in the planting pots was numbered according to
its grid position and labelled. The reproductive organs were harvested
first, followed by the leaves, stems and roots. These separate organs
were placed into corresponding envelope bags. The root samples were
individually placed in a 2-mm nylon mesh sieve and washed with tap
water. Afterwards, all the samples were dried at 65 °C (for 72 h) until
reaching a constant mass. The aboveground biomass of an individual plant
included the seeds, stems, and leaves, and the belowground biomass
included only roots for most species; the exception was L.
chinensis , whose belowground biomass included both rhizomes and roots.